Do you ever wake up in the middle of the night and lay there for ages trying to get back to sleep? Counting sheep doesn’t work and after much tossing and turning you just end up getting annoyed. The more you try to get back to sleep the harder it is.
I remember those nights well but I put it down to having kids and working unsociable night shifts in a nursing home. My body clock was all over the place and sleepless nights were the norm.