First of all, I apologize if this question does not belong on biology.stackexchange.
I've long been interested in sleep and recently postulated this question in light of reading about neuromodulators.
I noticed that for me, there can be at least two different kinds of sleep. One is the regular, nightly sleep where I go to bed, experience a light non-rem sleep onset in 15-30 minutes, then lose consciousness and become briefly aware 2-3 hours later, recalling episodes of dreams. The experience of falling asleep is sometimes unpleasant, sometimes tolerable. I can toss and turn around for some time. The desire to move and find comfortable position, followed by a loss of consciousness is the defining characteristic of this sleep (at least in the beginning)
Over the years, I've experienced another kind of sleep, which typically happens in the middle of the day, and it's onset is much more rapid. It's a pleasure to go to bed, the body becomes very warm, I can only describe this as pleasant burning. There's only a partial loss of awareness - I can listen to an audiobook while falling asleep like that, register words, but cannot put them together in sentences or remember them. If I hear the same audiobook chapter later, I remember only bits and pieces of the book. I'm aware of laying in bed, and potentially can awaken at any moment. Dreaming is sometimes observed, and takes place about 1.5 hours later, as with regular dreams. Alltogether, it is possible to spend up to 4 hours in a bed like that, with pleasure, and partial awareness of being in bed as a profound marker of this kind of sleep. I can stay in one position for over an hour, without moving.
A while ago I read a book on metabolic types, which may or may not be correct, and it described this kind of experience as "adrenal exhaustion", where adrenal glands become over-taxed because of sugary foods or refined sugar and result in this "crash".
I'm wandering if there's a term for the "more pleasant, daytime sleep" that I'm describing. Could this be related to the neuromodulator levels? Is there really such thing as "Adrenal exhaustion?"
I would appreciate your comments, keywords, or scholarly paper references that deal with different kinds of sleep.