I heard many years ago that late physical activities, for instance sport activities or even sex prevents the people from sleeping. I never had such problem until recent days. The day before I went for my running and it was almost 18:30 and few degrees below zero. I was fine during the entire time but when the sleeping time came, my difficulty emerged.
Of course the state of mind is very important too, as well as what is eaten and when but this lack of sleep with all involved factors comes to me at times. I once wanted to try something to help me sleep but have not thought about that seriously.
(Photo: This is Memorial Dr. in Calgary at the north bank of Bow River in last weekend when I went for running. No problem with sleeping since an early afternoon time had been selected. I did not go today due to the issue explained above)