Focus on Fatigue

Focus on Fatigue, Issue 41: Sleep inertia

By May 10, 2016 No Comments

Welcome to Focus on Fatigue,

The middle of the year approaches and, here in Australia, that means the onset of winter. With the days growing shorter and the nights chillier, this can be a good time to catch up on some sleep. This is especially true if you’ve been experiencing prolonged periods of grogginess, known as sleep inertia, when you first wake. This month we will examine the problem of sleep inertia. What is it? What causes it? And how can we reduce its effects?

It has been an exciting time at InterDynamics, as we recently released FAID Quantum, a new product in the FAID suite. FAID Quantum is a quantum leap forward in bio-mathematical modelling for fatigue risk management. For more information please see the InterDynamics News section below.

The FRMS Team

InterDynamics - Navigating Complexity. Delivering Clarity.

InterDynamics Pty Ltd
320 Adelaide Street Brisbane Qld 4000
Tel +61 7 32298300

Views expressed in articles and links provided are those of the individual authors, and do not necessarily represent the views of InterDynamics (except where directly attributed).

Feature Article

Give me a moment, I just woke up!

We all know that groggy feeling we get right after we wake up. It can include disorientation, confusion and continued sleepiness. This is the time when many of us stumble out to the kitchen mumbling about needing coffee. This period of time, where we make the transition from being asleep to being fully awake, is known as sleep inertia. It can last from just a few minutes up to four hours, though in most cases it will dissipate within half an hour.

Sleep inertia isn’t so bad when the most important task you need to undertake is getting from the bed to the bathroom. However, if you are abruptly woken from a scheduled nap at work and must immediately make important decisions or perform high-level tasks, sleep inertia has the potential to put you and your colleagues at risk of injury. This article will discuss some of the factors that impact the length and severity of sleep inertia, and ways in which we can reduce its effects.

Weighing up the risks and the benefits

Some shift workers are on the clock for days at a time. It is essential that these workers get enough sleep (including sufficient deep, slow wave sleep) to perform at their best and avoid the effects, and potential dangers, of sleep deprivation.  However, the effects of sleep inertia can also be severe. Indeed, when suffering the effects of sleep inertia a person may actually be less capable of performing work tasks than they would be if they’d not slept at all.

For workers who face the possibility of being awakened from a nap by an emergency that may require them to perform at high levels almost immediately, it can be difficult to determine the best timing for naps. Hopefully, the following information will assist in striking a workable balance between getting enough sleep, and dealing with sleep inertia.

Sleep inertia will often be worse if…

You are forced to wake up rather than waking up naturally – Being woken up by an outside force, such as an alarm clock, increases your chances of being woken during slow wave sleep and this creates worse sleep inertia than if you are woken during other sleep stages. REM sleep, the sleep stage where you experience dreams, can produce moderate sleep inertia, while waking during the lighter stages of sleep (stage one or two) causes the least sleep inertia.

You sleep for greater than 20 minutes but less than 90 minutes – This comes back to the chances of waking during slow wave sleep. If you nap for less than twenty minutes then your body doesn’t have a chance to filter down into slow wave sleep, so you’ll still be in the lighter sleep stages when you wake. If you sleep for a full ninety minutes then your body has a chance to go down through all the stages of sleep and come back up into light sleep in time for you to wake up. Some research has found that naps of around fifty minutes are most likely to result in severe sleep inertia.

You are in a circadian low when you wake up – Your body naturally wants to be asleep during circadian lows and it’s not too keen on being woken during these times. Therefore, waking during a circadian low will usually produce worse sleep inertia. The strongest circadian lows generally occur between 2-4am and 1-3pm, though there is some variation depending on if you are a morning or evening person.

You are already sleep deprived – A sleep deprived body is highly motivated to catch up on sleep. Therefore, if you are suffering from major sleep deprivation, this will often result in more severe sleep inertia.

What kinds of activities are affected by sleep inertia?

Sleep inertia does not affect all tasks equally. Generally, more complex tasks are affected more than simple tasks. For example, tasks involving speed are less affected, but accuracy may be a problem. Cognitive tasks, such as decision making and tasks involving high levels of concentration, are greatly affected by sleep inertia.

Self-monitoring is also affected by sleep inertia. Researchers have found that subjective sleepiness is not a reliable indicator of sleep inertia. It can also affect how well an individual rates their own performance on a task. So there may be times when you experience sleep inertia without realising it, or times when you underestimate its affect.

What can we do to combat sleep inertia?

Time your naps – If you’re having a scheduled nap at work, it’s best to stick to a maximum of twenty minutes, or sleep long enough to complete a full sleep cycle (about 80-100 minutes depending on the individual).

Time your naps, part two – Avoid scheduling naps during circadian lows (2-4am and 1-3pm) if possible.

Give it time – If you are woken in the middle of a sleep cycle, give yourself sufficient time to recover from sleep inertia before recommencing work. In the absence of major sleep deprivation, the effects should dissipate within 30 minutes.

Have a cup of coffee – Caffeine has been found to reduce the effects of sleep inertia in psychomotor vigilance tasks.

Avoid accumulating a sleep debt – If you are generally well-rested then you are less likely to suffer long periods of sleep inertia when you wake from a nap.

Use external stimulators – Turn on the lights, turn up some music, wash your face with cold water, or do some stretches. It has been suggested that these sorts of simple behaviours can help counteract sleep inertia, however, the effectiveness of such behaviours has not necessarily been proven.


  • Newman, R. A., Kamimori, G. H., Wesensten, N. J., Picchioni, D. and Balkin, T. J. (2013) Caffeine gum minimizes sleep inertia. Perceptual and Motor Skills, 116, 280-293.
  • Ikeda, H. and Hayashi, M. (2010) The effect of self-awakening from nocturnal sleep on sleep inertia. Biological Psychology, 83(1), 15-19.
  • Tassi, P. and Muzet, A. (2000) Sleep inertia. Sleep Medicine Review, 4(4), 341-353.
  • Signal, T. L., van den Berg, M. J., Mulrine, H. M. and Gander, P. H. (2012) Duration of sleep inertia after napping during simulated night work and in extended operations. Chronobiology International, 29(6), 769-779.
  • Brooks, A. and Lack, L. (2006) A brief afternoon nap following nocturnal sleep restriction: Which nap duration is most recuperative? SLEEP, 29(6), 831-840.
  • Ferrara, M. and De Gennaro, L. (2000) The sleep inertia phenomenon during the sleep-wake transition: Theoretical and operational issues. Aviation, Space, and Environmental Medicine, 71(8), 843-848.
  • Van Dongen, H. P. A., Price, N. J., Mullington, J. M., Szuba, M. P., Kapoor, S. C. and Dinges, D. F. (2001) Caffeine eliminates psychomotor vigilance deficits from sleep inertia. SLEEP, 24(7), 813-819.

InterDynamics News

New Product Release: FAID Quantum

InterDynamics FAID software has been an industry standard for alertness prediction and fatigue management since its introduction in the late 1990s. Now InterDynamics is setting a new standard with FAID Quantum, which offers a whole new level of scientifically-verified accuracy based on real-world data.

FAID Quantam has been developed by Dr David Darwent in conjunction with Professor Drew Dawson and Dr Greg Roach of the Appleton Institute. It uses the best sleep-wake predictor algorithms that have yet been published in international peer-reviewed literature and analyses the work-rest schedules of your personnel to produce a fatigue score in the Karolinska Sleepiness Scale (KSS). It also includes output in the original FAID scale for comparison.

Improved accuracy from better data

The researchers at the Appleton Institute have used what may be the largest database of quality sleep-wake data in the world, incorporating nearly 15,000 days and nights of data collected from various industries, including long-haul aviation, to underpin predictions.

With older bio-mathematical models of fatigue, predictions were based on average patterns of sleeping and waking but, with FAID Quantum, actual sleep and wake patterns are used to predict future alertness.

With this superior real-world data, FAID Quantum can justifiably claim to be the most accurate predictor of alertness available on the market today.

Versions and tools to suit your organisation

FAID Quantum is a cost-effective management tool with different options available for different sized organisations. It is easy to use for large data sets, giving quick calculations for multiple workers.

It can be integrated with third party rostering tools or FAID Quantum Roster.

Using the same interface as FAID Standard, it is easy for your organisation to upgrade.

FAID Quantum goes beyond safety compliance to best-practice prediction. While the ultimate vigilance of FAID Quantum is reassuring for aviation and other sensitive industries, the software also brings benefits in the smarter management of work schedules. This needn’t mean more or fewer staff but allocating your existing staff in ways that are better for them, better for safety and better for business efficiency.

For more information about FAID Quantum, please contact InterDynamics.

Conferences and presentations

This section outlines recent and upcoming InterDynamics speaking engagements and/or conferences that we recommend and will be attending.

In April, InterDynamics headed off to conferences in both Montreal and South Carolina. Details are given below:

FMAS2016 (Symposium on Fatigue Management Approaches) – International Civil Aviation Organization

5-8 April 2016, Montreal, Canada

The Fatigue Management Approaches in Aviation Symposium was convened by the International Civil Aviation Organization (ICAO) from 5 to 6 April 2016 in Montréal, Canada. The event provided an important information sharing opportunity for rule-making authorities, airlines, air traffic service providers, international general aviation operators, international helicopter operators, and all aviation professionals involved in safety-related activities.

Following the symposium, ICAO hosted the 2016 Conference of the FRMS Forum from 7 to 8 April 2016. This meeting developed themes related to the regulation and implementation of Fatigue Risk Management Systems (FRMS) in a flight operations context. The content had high relevance to operators and regulators alike and will provide unique insights for States and other service providers considering the implementation of FRMS.

2016 Crew Management and Timekeeping Conference – Norfolk Southern Corporation

10-13 April 2016, South Carolina, USA

This was the annual North American Rail Industry Conference. It facilitated the railroads to share and compare benchmarking data of Crew Management and Timekeeping.

The conference also provided opportunity for railroads to share their progress and practices when implementing Fatigue Risk Management Solutions. InterDynamics is a regularly invited attendee to share with the conference our products and services that can support the railroads.

In the News

Provided below are a selection of articles from around the web on the issues associated with fatigue. We hope you find them useful and interesting.

Article: What is Sleep Inertia, and How Can I Beat It

by Victoria Phillips, HuffPost Healthy Living (9 July 2015)

If you’re like most people, the first 15 minutes after you wake up aren’t your finest moments. Aside from morning breath, bed head, crusty eyes and grumpiness, you’re not firing on all cylinders, mentally speaking, right after getting out of bed. This transitional state is known as sleep inertia.

Video: Why is Waking Up So Hard

DNews (14 March 2015)

Do you have a hard time waking up? You’re not alone!  This short, humourous video gives a quick explanation of the causes of Sleep Inertia.

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