Conventional wisdom within sleep medicine says 7 to 8 hours of sleep is ideal. Less than 5 hours or more than 9 hours is associated with much higher rates of depression, diabetes, stroke, and dying in general.
Then why is it that some people feel great after sleeping only 4 to 5 hours, but feel terrible if they sleep 7 to 8 hours? In many cases, they’ll just wake up automatically after 5 hours without any alarms. Here’s one possible explanation:
Normally during sleep, you’ll go through 4 to 5 sleep cycles. In the beginning of the night, you’ll spend more time in deep sleep (or slow wave sleep, stages 3 and 4). Notice with each cycle, stages 3 and 4 get shorter and shorter, while stage REM gets longer and longer. Around the 5 hour mark, notice that the REM period begins to lengthen significantly. (Note: recently, stages 3 and 4 have been combined into N3).
Stage REM (rapid eye movement) is when you’re dreaming. A peculiar aspect of REM sleep is that your entire body becomes paralyzed, expect for your eye muscles and diaphragm. Rapid eye movements are seen when you’re dreaming.
Whether or not you have obstructive sleep apnea, if you are susceptible to sleep-breathing problems, you may have a prolonged period of obstructed breathing during the first long period of REM, which happens to coincide around 5 hours. Lack of muscle tone in your throat during REM sleep can be a problem if you have small airways from having a small mouth. Three to six AM is also when people with OSA are most likely to have heart attacks.
I’ve also had patients tell me that their sleep quality improves after taking an antidepressant. The interesting thing about antidepressants is that many of these medications lower REM sleep significantly. So the less often you have choking and apneic episodes during REM sleep, the better you’ll feel when you wake up. REM sleep is associated with creativity and certain types of memory. However, REM deprivation may be a small price to pay for waking up more refreshed after only 5 hours of sleep. We also know that prolonged REM sleep deprivation can lead to hunger, anxiety, irritability, and difficulty concentrating.
Are you someone who wakes up more refreshed if you sleep only 4 to 5 hours? What happens to you when you oversleep?