I've been having a very weird problem for a long time. The problem is:
I cannot sleep at night if I haven't taken a nap. Its opposite is also true which is: I sleep really well at night if I had a good nap that day. Even though I feel comparatively more tired at night on days when I don't take nap, still it gets difficult to sleep that night.
It's as if my biological clock repeats what happens in the afternoon at night !!