I've always been able to get to sleep easily and quickly, as a rule but there are always the odd exceptions for one reason or another. When I was in the Army, I could drift off in the back of a deuce-and-a-half bouncing down the road. Like Lolo said, once asleep usually my sleep is deep and undisturbed, and less often, it is choppy and interrupted where I wake up and go right back to sleep 15 or 20 times. Fortunately, those are in the small minority.
When I was working, I was usually in a job position that required that I take one full hour for lunch. It doesn't take me an hour to eat. So, I developed this pattern where I would take my morning "coffee break" as late as possible, eat my lunch, then when my actual off-the-clock lunch time came around, I would go out to my car and take a nap for 45 minutes or so. I'd read a book for maybe 10 minutes beforehand, and get very drowsy. I had a little travel alarm clock in the car that I would set, but often I would just wake up naturally and go back in to work refreshed. I would say, 9 times out of 10, I would feel refreshed. On that 10th time, I might feel a bit groggy for a few minutes or so after I woke up. I did that for 25 years or more and it got to be kind of an office joke. One version was, Question: "Have you seen Gary? Answer: "Have you looked in the back seat of his car?" (because my actual lunch time didn't always start at the same time every day).
So, with the daily nap routine that set in for so long, now that I am retired, I often get drowsy in the afternoon and go upstairs "to read."
My wife often has an awful time getting to sleep. She has told me she just can't seem to turn her brain off; she lies there in bed and continues to think about this or that. It's been said that intelligent people sometimes have this problem; I guess we know where that puts me.