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Sleep Inertia: How long does it take you to wake up really?

“I get a good night’s sleep but I don’t feel refreshed when I wake up.” I used to hear that a lot back when I was coaching people towards better sleep. There are a rare lucky few who can fall into a deep slumber as soon as their heads hit the pillow and wake up eight hours later all bright eyed and bushy tailed. I used to explain to my clients that it is not reasonable to expect peak performance moments after waking up. Transitioning from being awake to being in deep sleep takes some time, normally between 30 and 45 minutes. The brain enters a dramatically different state in deep sleep. Brainwaves slow down and become more synchronized. In the images below you can see just how different a person’s brainwaves look when they are awake compared to when they are in deep sleep (stages 3 and 4).

I would continue coaching my clients by saying “If your brain takes some time to get into deep sleep and deep sleep is a dramatically different brain state, it is going to take some time to get out of it and back to an alert state of high performance.” You should feel pretty good, and be functioning at a high level, within 30 minutes to an hour after waking up. But of course this does not make it any easier to get out of bed, especially if your alarm clock leaves you feeling groggy and fatigued. This is because of ‘Sleep Inertia’ [1]. Remember your high school physics –a body in motion will stay in motion unless acted upon by an external force? It’s similar with sleep. A brain in a state of sleep wants to stay asleep. Can you relate?

Sleep inertia can have more serious effects than grogginess and fatigue. Most people feel confused and disoriented for a few moments right after waking up. Some can even be at sub-par levels when it comes to psychomotor and cognitive skills. Think about how wobbly you were as you stumbled out of sleep to your last midnight bathroom break or how well you solved your child’s math problem when they woke you up in the middle of the night. That’s sleep inertia at work.

We can usually muddle through our morning routines until sleep inertia wears off without many problems. But what happens when your partner catches you napping on a lazy weekend afternoon instead of cutting the grass? It’s pretty hard to jump to attention and start up the ol’ John Deere right after being caught. Or worse yet, what happens if you are 35,000 feet in the air and you have to react quickly after a nap? When I was the human fatigue specialist with the Transportation Safety Board of Canada (TSB), we investigated an incident where this exact thing happened [2]. The aircraft was crossing the Atlantic during the hours of darkness and, feeling fatigued, the first officer took a nap. Napping, also known as ‘controlled rest’ in the aviation world, can be an effective fatigue countermeasure, providing that the effects of sleep inertia are managed. Studies have shown that sleep inertia can last 30 minutes and sometimes even longer. During this period, a pilot’s reaction time, logical reasoning and ability to process visual information can be less than stellar. This means you can’t expect a pilot to perform really well moments after controlled rest. Unfortunately, the first officer crossing the Altlantic became actively engaged in flying very quickly after waking up, and still subtly confused by the effects of sleep inertia, pushed forward on the control column to avoid a perceived collision with an oncoming aircraft. Fourteen passengers and two flight attendants were injured in the ensuing pitch excursion.

Fatigue Risk Management Systems (FRMS) that prescribe controlled rest as a countermeasure to reduce the risks associated with becoming fatigued while on duty, should permit a sleep inertia ‘dissipation duration’ of at least 15 minutes before the person is reengaged in duty.

I have a few more tips for anyone considering adding napping to the FRMS.

  1. Limit naps to 20 minutes (see my last tip for an alternative). Napping for longer than 20 minutes can allow the person to enter deep sleep and to then wake up from deep sleep. Sleep inertia lasts longer and the effects are worse when you wake up from deep sleep.
  2. Avoid napping between 22:30 and 04:40 hrs. This is referred to as the ‘circadian rhythm trough’ and the biological drive to sleep is highest during these hours. This makes it hard to shake off the sleep inertia after napping and return to an alert state.
  3. Don’t rely on napping to make up for lost or poor quality sleep. By this I mean don’t short change your sleep with the idea that you can nap on duty to make up for it. You will run the risk of entering deep sleep during your nap. Always ensure that you get between seven and eight hours of good quality sleep every day.
  4. Keep the duty durations reasonable. Don’t use naps to extend your duty day. Staying awake for longer than 17 hours increases the risk of fatigue and if naps are used that late in the day, sleep inertia can be worse.
  5. Consider supplementing the nap with a moderate amount of caffeine. One coffee or energy drink (80 – 100 mg of caffeine) taken just before a nap may stave off the deep sleep and the stimulating effects should kick in by the end of the 20 minute nap. This can help you return to an alert and well performing state. Be careful with this tip. I don’t believe that caffeine [3] should be used as a substitute for sleep and the last thing an FRMS wants is a team maintaining alertness by Red Bull.
  6. Explore technology that can accurately detect deep sleep and wake people up from light sleep. The idea here is that longer naps, especially those with deep sleep, provide more fatigue fighting power. So if you can nap for 90 minutes and transition from light sleep to deep sleep and then back to light sleep before waking up (known as one full ‘sleep cycle’), you will be less likely to become fatigued during the rest of your duty than if you only slept for 20 minutes. The problem is that you can’t program your brain to wake you up during light sleep. You need some form of deep sleep detection technology that ensures you will not wake up from deep sleep but rather wake up from light sleep. This will lessen the effects of sleep inertia. Be sure to check with a human fatigue specialist before you adopt this techno-tip. There are lots of apps and gadgets that claim to accurately detect deep sleep with very little scientific evidence to back them up.

References

[1] The term “sleep inertia” was coined by Lubin et al. in 1976; see Lubin, A., Hord, D., Tracy, M., & Johnson, L. (1976). Effects of exercise, bedrest and napping on performance decrements during 40 hours. Psychophysiology, 13, 334-339.

[2] See the TSB Aviation Investigation Report A11F0012, Pitch Excursion, Air Canada, Boeing 767-333, C-GHLQ, North Atlantic Ocean, 55°00’N 029°00’W, 14 January 2011.

[3] To learn more about caffeine see Caffeine – Beware the Insidious Effects of Caffeine at http://sleepanddreams.com/?p=129.

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