there are 4 sleep phases, the first 2 are basically just chill out time, the other 2 are forms of Deep sleep REM(Rapid Eye Movement) sleep is the deep sleep that repairs your Brain, Delta sleep is the deep sleep that repairs your body. If you are lazy, you wont spend much time in Delta or REM. If you do physically demanding work all day, you will have longer Delta sleep, and less of everything else. If you do something mentally demanding all day, you will have mostly REM sleep. If you are both physically and mentally active in the same day, you will have closer to 50% REM and 50% Delta, and the other 2 are very short transitinal phases, but thats pretty extreme. But on avg it works out that most healthy people get about 25% of each of the 4 sleep modes. The guy who holds the world record for longest time being awake ( i think its 9 days, not sure) they monitored him when he went to sleep, he slept for 14 hours and spent almost exactly 7 hours in ech of the deep sleeps, and almost no time at all in the lesser sleep modes. The cycle in which you go through all 4 phases takes on avg 90 minutes, REM is the last one in the cycle, which is why it always seems like you have dreams right before you wake up. Delta is the hardest to wake up from, because your body is in its most dormant mode it can be, if your woken up in the middle of Delta, you feel like crap.
