Often when trying to sleep after a long period of deprivation, it feels different, in that I can actually feel individual systems switching off -- I might have

Often when trying to sleep after a long period of deprivation, it feels different, in that I can actually feel individual systems switching off -- I might have music playing through my head but be incapable of conscious (subvocalized) thought, or vice versa, but if I'm aware of anything other than breathing, then I'm far from sleep. And, after a few hours of lying in bed trying to sleep (knowingly without success), I might suddenly feel wide awake to a greater extent than what would be expected from normal sleepiness/wakefulness cycles. This finding jibes well with my experiences.