Why do brainwaves slow down?

So from experience with WILDING i know we can be at full alertness during the times we should be asleep. Some dream yoga practices lead to awareness even in the deepest parts of dreamless sleep.
With all this in mind i wonder, why do we fall unconscious anyways? We are perfectly fin staying in alpha- beta range throughout the day. Does melatonin cause the levels to drop? What is the correlation of body falling asleep with mind falling asleep?

Hi Dramr777,

Melatonin (the sleep hormone) is what helps our body shut down in the night. We do this because without it, our circadian rhythms would be screwed up our whole life and none of would have a good night’s sleep. We fall “unconscious” every night as a result of these two things working together. The part of your brain that is activated during lucid dreaming is the same part that uses your senses. This is why we are somewhat “alert” when we should be dreaming.