In school I learned that people sleep in 90-minute cycles, but that this was an average and that if varies widely from person to person. How could I find out what my sleeping cycle is?
I would say : by noting how long you have slept when you wake up spontaneously and search for a pattern. For instance, if you often wake up after having slept for roughly 2h, 4h and 6h, one could suspect your cycles are 2h long or so.
That’s how I found out that the duration of my sleep cycles was indeed around 90 minutes…
The sleep cycles refer to the different phases of sleep. There are various phases, the deepest phase (and the part of sleep wherein we dream) is REM sleep: rapid eye movement. Studies of people sleeping show that your eye moves during REM sleep, as you are watching your dream. You cannot act out your dream because of certain paralyzing features during sleep (unless you are a sleepwalker). REM sleep increases in duration during a night’s sleep. There are usually four cycles, and the last cycle of REM is the longest, lasting about 90 minutes. But the prior cycles are shorter.
These phases can be demonstrated on an EEG (electroencephalogram) on a sleeping person. For more info, search “REM” or “sleep +REM.” Report back.
This states there are five stages of REM and four stages in sleep.