For me it’s always stress but I have a long history of sleep related anxiety. Like fighting addiction to prescription sleep meds levels. I very rarely have a truly great night of sleep. Most of the times it’s just “good enough.” Sometimes I sleep well without taking anything. Sometimes I barely get by. I use, cut in half, 1mg melatonin to help me get to sleep sometimes if I’m not tired enough (you only naturally produce not even half a milligram so even 1mg is a lot to your body and taking too much can have an opposite effect). Other times I take it when I inevitably wake up in the middle of the night. Usually after about 3-4 hours like clockwork. Then my body doesn’t always want to go back to sleep. I have other prescription meds that I use occasionally as well. It’s not addictive like the stuff I used to use and I only use it ever now and again. Its all 100% stress induced though. All of it. The more pressure I feel to make sure I sleep well the next day the harder it is. I know everyone experiences this to some degree but my brain takes it to a new level. Years ago it would get so bad I’d have to go sleep in another room or on the floor because I just had to “go somewhere else.” Then I changed jobs and was much happier for a while and it all went away for some years until just recently works going down the shitter and society is literally falling apart around me.