1) All sleep can be divided in two categories: REM sleep and NREM sleep.
2) REM (Rapid Eye Movement) sleep is the best time to wake up. Also, if awoken during REM sleep, people tend to remember their dreams. It generally comes every 70-90 minutes, with cycle getting progressively longer as the length of time spent sleeping increases. It can go up to 120 minutes. Find your own individual cycle by trial and error, but typically 1.5 hours works for most people. Therefore, try to sleep the number of hours divisible by 1.5 (e.g. 1.5, 3, 4.5, 6, 7.5, 9)
3) NREM (Non Rapid Eye Movement) sleep is subdivided into four stages.
- First stage. During the first stage the person is just falling asleep, it's very short. Person can be confused if woken up during this stage.
- Second stage. About half the time spent sleeping is the second stage. Not the best time to wake up, but bearable.
- Third/Fourth stages. Delta sleep. This is when people have nightmares, sleepwalk, get sleep apnea. Hard to wake up during this time. Not recommended.
4) Therefore, the best thing is to wake up during REM sleep, and calculate it as happening at approximately every 1.5 hours and correct through experience. One episode of REM sleep lasts about 5 minutes.
5) Here is a diagram for your convenience.
I just wrote it in Russian at another board, and decided other people might find this information usetful too... I know that there is a neuroscience specialist on my friend list *waves* Feel free to correct me if I got something wrong. It has been a while since I took the exam in it, and it has never been my favorite part. Nothing CNS has ever been my favorite part...