I was in a dilemma whether I should put this in my science blog or here with the mainstream stuff, but I figured it is interesting and affects everyone so why not. The ideas were transported to me through Patrick when he attended the recent APS Conference (physics). So a guy gave a talk about sleep. They found out that there are 2 main stages in sleeping, the deep sleep and the rem (rapid eye movement) sleep. There is a cycle of about 1.5hours, which consists of 1h 15min of deep sleep and 15min of rem sleep. The cycle repeats about 4 or 5 times for a total of (say) 6h or 7.5 hours of sleep.
During the deep sleep is when the brain and the organs "shut down" to get rest. In fact, not all organs shut down at once but there is a sequence: 1st this organ, 2nd that organ, etc. The last organ to shut down is the heart, after about 5 hours of total sleep. That means if you sleep lees than that you are not resting your heart for that day.
The most interesting part though has to do with rem sleep. This is the stage at which memory is written in the brain - all the thoughts, the inputs, the stimuli are recorded during rem sleep so that you can remember tomorrow and in the future. This is a stage at which the brain is not is low power mode: it is quite active to store all these information.
This is the best time to wake up!
If you wake up during deep sleep you will feel tired, not enthusiastic and bored. However if you wake up during rem sleep, you like feel almost perfect as if you weren't sleeping, even if you had less total sleep!
For example it is better to sleep 4.5h and wake up during rem sleep rather that keep sleeping for 1 more hour and then wake up during deep sleep. This absolutely works with me because sometimes I sleep a lot and I still feel tired (obviously I woke up during deep sleep) and other times I sleep 4-5 hours but yet I wake up and feel perfect (I woke up during rem sleep). My previous theory was that if you sleep short enough then your brain does not fully enter deep sleep and so if you wake up again soon enough you will feel ok because it is as if you never slept. However I must admit this new evidence is better:-)
They also note that the duration of rem sleeps varies during the night. The first one is the shortest, and the last one is the longest. This also explains why afternoon naps (said to compensate for lack of night sleep) can never replace night sleep: there is not enough time to get into rem sleep and record new info in your brain; you may get some rest but you will lose the memory recording process.
