When a Good Nap Goes Bad
May 10, 2013by Kerry Potter
After doing a little bit of investigation about sleep myself, I think I understand how a nap can be beneficial sometimes and other times not be appropriate.
First, let me explain how a sleep cycle works. There are five stages of sleep. The first four stages of sleep are considered Non-Rapid Eye Movement (NREM) and the fifth stage is Rapid Eye Movement. To complete a full cycle of sleep, all five stages, takes about 90 minutes, but can last up to 120 minutes. Light sleep occurs during stages 1 and 2. This is where most people remain (or at least should) when taking a powernap.
In stage 3, deep sleep begins. During stage 3 and 4, blood pressure drops, breathing becomes slower, and muscles become more relaxed. Essential hormones such as growth hormone are also released during these stages. (sleep foundation citation)
During stage 5 sleep, also known as REM sleep, dreams occur. We spend about 25% of the night in REM sleep. This part of sleep is very important because it provides energy to the brain and body and cortisol levels dip during sleep in order to promote alertness during the daytime.
When nap length remains under 30 minutes, most people will remain in a light sleep. It is very important to remain in these cycles during a nap in order to improve cognitive function, reaction times, and overall efficiency.
When naps last longer than an hour (which mine usually do), our bodies enter the latter sleep stages, slow wave sleep. This is important when sleeping for a full six to nine hours, however, during a nap slow wave sleep can backfire on us. Waking up after entering slow wave sleep means the body will crave more sleep, leaving you tired and groggy and your muscles feeling heavy. Excessively long naps can through off your circadian rhythm and hormones.
Naps can leave people with sleep inertia (basically feeling like a slug), especially when they last more than 10–20 minutes. The feeling of grogginess and disorientation that I often experience when waking from naps comes from getting up during the midst of a deep sleep. The National Sleep Foundation states that this feeling should usually only last for a few minutes, but can be much more severe in people who are sleep deprived or who nap for extended periods of time. I also think individual’s genetics play a key role in how people respond to naps.
Research shows a nap lasting 30 minutes or longer is more likely to be accompanied by sleep inertia.
So I have found that I was going about my naps all wrong. Usually, I would end up sleeping over an hour, typically 75 minutes and very late in the afternoon around 5 or 6 pm when returning home from work. Taking naps that late in the day was probably throwing off my circadian rhythm and setting me up for a bad evening.
I think sleep is such an interesting and underrated topic. So I hope this article gives you a little bit to meditate over. For more information about the topic of sleep, the National Sleep Foundation is a great resource!