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.

I won’t try to quantify exactly how much sleep one needs since it differs for each person, but rather explain some of the factors and what people can do in order to optimize their sleeping pattern.

The REM Cycle

During sleep, the body goes through stages of light and deep sleep.  Generally speaking, these types are known as rapid eye movement (REM) sleep , and non-rapid eye movement (NREM) sleep.  The NREM type consists of three different stages, or cycles of sleep known as N1, N2, and N3.  The names of each type are not really important in the context of this article, but the body moves between these stages during sleep and each stage serves a different function.

On average, each sleep cycle last 90 to 110 minutes.  When one wakes up in between a sleep cycle, they will feel tired when they wake up.  A lot of times, the sleep cycle gets interrupted when the alarm clock rings in the morning.  But when one wakes up at the end of the cycle, they will feel very refreshed.

The time to optimize here is plan the sleeping time in accordance with the sleeping cycle to ensure that one will wake up at the end of a sleep cycle.  Of course, this will take some experimentation to gage exactly how long each sleeping cycle is.

My method involves leaving some extra time to wake up.  I overestimate the time it takes me to fall asleep and the time it takes for one sleep cycle, I will wake up feeling refreshed before my alarm clock rings.  However, having too much extra time will cause the body to start its next cycle before waking up, but that depends on the person and their sleeping pattern.  Again, this takes experimentation.

Another issue is how long to sleep for.  To me, this doesn’t really matter as long one is able to wake up naturally.  This way, the body is able to communicate that it has had enough sleep.  Although, there are times where people wake up prematurely from sleep and feel that they need more sleep.  Another way would be to see if someone can get through the day without feeling tired or falling asleep.

Circadian Rhythms

Circadian rhythms are why we should not sleep whenever we want.  This is just a fancy term for explaining that each person’s body maintains the same pattern everyday.  Below is a picture from Wikipedia of what happens throughout the day for the average person.

A lot of these events don’t really have to do with sleep except for a few.  For example at 4:30 AM, our body should be at its lowest body temperature if the above pattern is followed.  Wikipedia states the following:

The optimal amount of sleep is not a meaningful concept unless the timing of that sleep is seen in relation to an individual’s circadian rhythms. A person’s major sleep episode is relatively inefficient and inadequate when it occurs at the “wrong” time of day; one should be asleep at least six hours before the lowest body temperature.  The timing is correct when the following two circadian markers occur after the middle of the sleep episode and before awakening:

• maximum concentration of the hormone melatonin, and
• minimum core body temperature.

Six hours before the lowest body temperature would mean that the optimal time to go to sleep for the average human is at 10:30 PM.  I experienced this first hand.  I used to sleep at 4 AM until 2 PM and always felt that my sleep felt super restless, but now that I sleep from 8:00 PM to 4:00 AM (I chose to sleep at this time because this way I get to talk to people in Vancouver while I’m abroad), I feel super refreshed waking and most of the time, I don’t need an alarm clock to wake me up.  I only need the clock tell me what time it is.

Conclusion

This is what I follow when I plan my sleeping pattern.  I used to have a really erratic sleep schedule, where I woke up early one day and late the next because I’d always wake up in time to go to my first class of the day.  If the start time differed everyday, my sleeping time would change too.  As a result, I felt tired everyday and tried to adjust my sleeping pattern.  After changing up my habits, I no longer feel the need to take naps everyday, and I don’t feel fatigue anymore.

Sources

1. http://en.wikipedia.org/wiki/Sleep
2. http://en.wikipedia.org/wiki/Circadian_rhythm