Henry Poon's Blog

Sleep Debt and Optimal Sleeping Time

Sleep Debt

I’ve been tracking my sleeping and over the past little while and I’ve accumulated 12.7 hours of sleep debt (as of 5 Oct measured by the Sleep as an Droid app).  I got this value by taking the difference of my actual time slept and the actual amount of time I need for each day and added up all those numbers over two weeks.  I noticed that this sleep debt over several days stacks up more and more.  I ended up feeling less and less rested everyday.  It seems obvious, but I never really paid attention to it until now.

What I’ve been doing now is try to sleep earlier to “pay back” this debt (probably the right thing to do).  I did a quick search on Wiki about sleep debt and as it turns out, the article basically told me the same thing that I noticed myself.  Sleep debt indeed does accumulate and catches up.  For me, one or two days, it’s probably okay, but anymore than that, then I start feeling less rested everyday.

For a bit, I tried sleeping at 11pm and waking up at 7am to pay back this debt, but I soon came to realize that I still didn’t feel better even though I was in fact paying back this debt (albeit slowly).  I came to realize the problem was in my sleeping pattern.  I didn’t actually know how much sleep I needed or when I needed to sleep (i.e. circadian rhythms).  I had completely forgotten about it (I wrote something similar on the subject awhile ago).  I always knew it existed, but I guess I lost track of what it was after I came back from Germany.  As of right now, my sleep debt for the last two weeks –7.9 hours, which is a lot better than before.

Circadian Rhythms

After I bit of trial and error, I found my optimal duration and time to sleep.  Apparently, I feel best if I sleep for 7.5 hours at 2:30am and wake up at 10am.  When I woke up after doing that, I felt great.  Kind of a night owl’s sleeping pattern.  Apparently some people can in fact sleep for 6 hours a day and sustain this daily without the need for naps, but that is a small minority of the population.  I on the other hand, fall within the average.

This doesn’t really work for me since I need to be up at 7am to go to sleep.  So now, my solution is to shift my circadian rhythms forward.  I’ve read a method for people with DSPS (delayed sleep-phase syndrome) that involved pushing back my sleeping time later and later until I reached the time I wanted.  If I slept at 2:30am usually, I’d sleep at maybe 5:30am the next day, then 7:30am the next etc. until I reached my goal of 11pm.  It would mess up an entire weeks schedule but apparently it works.  I’m not saying that I have this syndrome (I’m not about to self diagnose here), but this kind of treatment seems kind easy to do at home without great risk.  I don’t really have a week to spare for this right now so that is automatically out of the question.

Another method involved bright lights.  The Harvard Medical School Guide to A Good Night’s Sleep (really good book on sleep by the way!) states the following:

This treatment grew out of the discovery that exposure to bright light within a few hours of the body’s low point in body temperature—which occurs during the overnight hours—shifts the circadian rhythm. A dose of bright light after the temperature minimum advances the circadian rhythm, while a dose before it delays the rhythm.

Knowing this, I can shine a bright light in my face every morning when I wake up at 7.  Hopefully, my circadian rhythm will slowly shift to this new time.  Once I do that, maybe I can wake up at 7am feeling well rested.

Although I try to sleep and wake up at the same time everyday, school work always tries to disrupt my schedule, and as a result, I haven’t paid off my sleep debt and my sleeping time is kind of inconsistent at times.  Life always finds a way to break it.

Random Analysis on My Sleep Cycle

As an aside, I tried to find out how long one of my sleep cycles were.  On average, they are 90 minutes long, but differ from person to person.  The app that I use for measuring sleep graphs out how deep/light my sleep is throughout the night.  Since the human goes through cycles of light and deep sleep overnight, I thought I could measure the time duration between.  I looked at some of my sleep graphs (similar to this one):


In this graph (from 9 September – there is a typo in the picture because I mixed up the dates initially), the blue graph shows how deeply I sleep through the night. The sampling rate for that measurement wasn’t very good with the trial version that I used at the time.  Three regions are shown where values of the blue curve above the blue line mean I’m awake, values between the green and the red line mean I’m in a period of light sleep, and any value below the red line means I’m in deep sleep.  As it is shown in the plot above, it seems that a huge chunk of my sleep is in deep sleep, which is really strange since I’m supposed to be going through cycles of light and deep sleep.  Here, I only see one instance of light sleep.  Not really sure what to make of it other than the fact that the app is not a robust way of doing such measurements.

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