SabbraCadabra wrote:
I would always try to get to bed by 4AM, but it would slowly drift further and further, until I would notice that the sun was coming up before I was asleep...so then I'd have to force myself to start going to bed earlier.
People and animals exhibit a natural, innate circadian rhythm, and the periodicity of that rhythm does not in all cases approximate natural day-length. If placed in a cave environment where there is no natural sunshine and no clocks, people's tendency to sleep and wake varies all over the place, with some having a shorter and others a longer day-length than 24 hours. These differences can cause a number of different sorts of sleep disorders.
In everyday life, we are "entrained" (re-set) by events such as a work shift, sunrise, television shows we regularly watch, and so on. (In my case, my cats, wanting to be fed in the morning!)
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