Phases of sleep

[dimamuzhetsky]

I hear during sleep humans constantly pass from a "fast sleep" phase into the "slow sleep" phase as far as I get it,each such a piece being somehow like 90 minutes long.What an interesting phenomena!Could You please shed more light upon it for me?Elaborating I mean into the depth of the question?Thank You

[grasscarp]

We have about 5 sleep cycles a night - each lasting about 90 minutes. You have different types of sleep, one which refreshes the body, slow wave, and the other refreshes the mind, and stores the information you have gathered during the day. The latter is called Rapid Eye Movement sleep, because your eyes are moving at that time, and it is also when you dream. For every hour you sleep you can stay awake for two hours, so when you sleep you accumulate credits - one hour equals two credits. You can have a sleep deficit, but cannot accumulate more than 16 credits (16 hours that you can be awake). It is an interesting subject.