This is really something in recent years; my sleeping troubles have been different in the past.
I rarely have problems sleeping; that said, I don't care that much for a "normal" day/night thing. I go to bed when tired, and usually fall asleep pretty quick. I don't lie in bed worrying about anything... aside from a few things, when just in bed "did I turn the stove off?" and "isn't the tap in the kitchen running?" (and those things I also worry about when leaving the house)
On average I sleep between 3 and 4 hours, and I'm up again. Might have a 15 minute powernap during the day. And I regularly skip sleep altogether. So, sometimes I go on for 2 or 3 days without sleep. Because I have stuff I want to do.
I tend to have a lot of manic bouts (where my creativity excels) and I try to make most use of those bouts; whether that's noon or 3 at night.
However, I do need my sleep. If I don't go to bed, when my body actually tells me to, my joints start to hurt, and I just need to lie down. Might be age, and unhealthy living habits. So, mostly physical pain.
I used to be a light sleeper, in the past, worry for hours, but life is, all things considering, pretty good now, so there's a lot less trouble sleeping