Andrew’s post about segmented sleep patterns reminded me of a documentary I saw a while ago. It was about the Pirahã people, an indigenous hunter-gatherer tribe living in the Amazon Rainforest following a similar pattern of multiple short naps throughout the day. I read some more about sleep research which I’m reviewing in this post and relating to my own experience.
I bought a sleep phase alarm clock some years ago. The alarm clock measures my movement at night with a wristband sensor and tries to wake me up during a light sleep phase. This means the alarm goes off up to half an hour before the time I set it to but it does so with the very pleasant sound of tweeting birds. Gone are the times when I was woken up by a horrible noise, provoking the urge to smash that alarm clock.
Convenient as it is, the sleep phase alarm clock does not make up for a lack of sleep. I think one of the main reasons I feel more refreshed in the mornings these days is that I am more aware of my sleep cycles. I always try to set my alarm to a wake up time which is a multiple of 90 minutes, the length of an average sleep cycle. There are 3 stages of non-REM (Rapid Eye Movement) sleep. Stage one is the transition to sleep and lasts about 5 minutes. In the second stage, lasting 10 to 25 minutes, heart rate and body temperature decrease. The third stage is deep sleep. It’s difficult to wake up people in that phase and when woken up they usually feel disoriented for several minutes. Blood flow to muscles is increased to restore physical energy. The REM sleep phase is first entered about 70 to 90 minutes after falling asleep. In this phase arm and leg muscles are paralyzed and most dreaming occurs then. However, this paralysis does not occur for some people and can lead to sleep behaviour disorders like sleepwalking. During a good night’s sleep (or two sleeps, for that matter) we go back and forth through these stages in cycles. Usually deep sleep occurs in the first half of the night. In the second half, REM stages are longer and we don’t go to the third stage anymore. This explains a sensitivity to waking up in the middle of the night or early morning hours, because that’s when we stay in the lighter sleep phases.
My alarm clock records the measurements and below is a diagram of my movements throughout the night of August 2nd. It shows how I started moving more and more towards the morning, indicating alternation between the REM stage and light sleep first and second stages.
Well, I think it’s time to get some rest. It will help me concentrate and remember tomorrow.