Perhaps more precisely, I seem to have three distinct but somewhat related mental states: normal sadness, normal my-brain-needs-sleep sleepiness, and this strange hybrid between the two that doesn't seem to have any specific cause and I can't get rid of by either trying to sleep or trying to cheer myself up.

And I almost never actually look forward to sleep - the only time I actually want to be asleep is when I've just woken up and am feeling this strange "fake sleepiness" in which I'm just lying in bed with my head in a fog, having no particular reason to get up but not actually sleeping either, conscious but not actually thinking about anything much. (It's kind of hard to describe these things.)