With good sleep linked with stable moods, a healthy weight and good memory retention (that is, all the good things), it’s worth understanding how sleep cycles work so you can give yourself your best chance of restful slumber.
The average sleep cycle lasts about 90 minutes, with your body cruising through different phases to help the brain and body rejuvenate for the next day’s adventures.
“We could think of it as a rollercoaster, where you go down through lighter sleep to a deeper sleep, then back up through lighter sleep again, across about a 90-minute period,” Emeritus Professor Dorothy Bruck, chair of the Sleep Health Foundation, tells Coach.
“There’s lots of individual variation … you might have four or five of those cycles [a night], punctuated by a period of rapid eye movement [REM] sleep, which is when we have structured dreams.”
Sleep changes as the night wears on
When you first lay down, you will start to drift through the four stages of NREM (non-rapid eye movement) sleep.
“You might fall asleep in 10 minutes, then go down through stage one, which is a very drowsy stage of sleep – sometimes you might have that on the couch,” Bruck explains.
“Stage two is what we call ‘real sleep’, where we see brainwaves associated with real sleep, then stages three and four are deeper sleep.”
At the beginning of the night you’ll only have short bursts of dream sleep, with much greater quantities of deep sleep, but as the night progresses, you’ll have less deep sleep and more dream sleep.
“We might only have five or 10 minutes of dream sleep in the first cycle,” Bruck explains.
“By the time you get close to morning, you could be having 20-minute episodes of REM, punctuated with a little bit of stage two and so forth.”
Why the different phases?
Our body is going through so much fascinating rejuvenation as we sleep, and Bruck says it seems each stage serves a purpose.
“There are lots of changes happening in the brain,” she explains.
“One thing that happens is that our neurons actually shrink in size, which allows the fluids that are around the neurons, which are like rivers, to widen and wash out the toxins that have accumulated during the day.”
At the same time, our brains are consolidating memories and sorting through problems.
“A lot of the cognitive [repairs] are happening in REM sleep,” Bruck explains.
“But sleep an integrated system that helps [mental] and physical restoration.”
How to nap best, in terms of sleep cycles
If you’re feeling weary, Bruck says it’s usually a good idea to limit your naps to 20 minutes so you don’t fall into a deep sleep, which is much harder to rouse from.
“We’re sort of thinking 10 minutes to go off to sleep, then have a 10-15 minute nap,” she says.
“In the normal course of events you won’t go into deep sleep in a 20-minute lie-down period.”
But if you are particularly sleep deprived, then Professor Bruck says you may benefit from a full sleep cycle nap — but there’s no need to set an alarm for 90 minutes (as some people suggest).
“It’s a bit simplistic because sleep structure during the day is not quite so predictable and it depends on how sleep deprived you are,” she says.
“If you’re going to have a nap in the morning, it’s going to have a lot more REM sleep. If you’re going to have a nap in the afternoon, it’s going to have a lot more deep sleep.”
So if you’re totally exhausted and have the luxury of a free morning or afternoon, then Bruck says you might be best to allow yourself to wake up naturally.
“If you wake up naturally, you’re less likely to have that sleep deprivation. Having said that, if you have a long afternoon sleep, you’re not going to be as ready for sleep that night when you normally are ready to sleep, so that is the downside of having a [long] nap.”