2 Major Factors driving your Sleepiness
1. The brain needs sleep and after being awake for approximately 16 hours the brains need for sleep drives your sleepiness force.
2, Evolution of humans has resulted in our body having multiple biological systems that follow the 24 hour circadian cycle, which results in our naturally waking up some time after sunrise and being sleepy sometime after sunset.
All shiftworks and international plane travellers are aware of this night time internal force for sleep, which is independent of the “brain needs sleep” factor and operates even if you sleep during the day and then start working at night.
Initially these above 2 basic biological forces can be resisted by being in an alerting environment, such as watching a thrilling movie or talking intensely with friends, or walking around or consuming stimulant drugs such as coffee. However as your continual period of being awake increases these drives also increase, with the brains need for sleep continually increasing, but the circadian sleep drive slightly and temporarily reducing in the morning but returning at even higher levels as the next afternoon arrives.
Basic normal Sleep Cycle
During a nights sleep the body goes through several sleep cycles. The sleep cycle in normal sleep lasts for approximately 90 minutes and then there is a short period of awakening, but being sleep impaired this short period is not remembered unless you are disturbed by either light, temperature, or noise.
The 3 key factors for Quality Sleep
Light Temperature Noise
The light of the moon or the rising morning sun, the noise of someone snoring or a dog barking and an big change in room temperature, each can not only fully wake you up at the end of a sleep cycle but can be powerul enough to wake you during some parts of the cycle itself.