Had sleep apnea before leaving the states. Used to sleep 14 hour days, still sleepy during the day. Didn’t figure it out until I got depression too and started examining the sleep issues as potential depression symptoms (they weren’t, and in fact sleep apnea sometimes causes depression).
Note my example is extreme, and I’ve seen many complaints about other issues (like waking up in the middle of the night, I never did), so ymmv
My nightmares largely stopped after being awake tired af and terrified of sleeping, when I said “damn you nightmares, you can’t scare me into sleep deprivation! I’m coming in there and I’m gonna fight back”, and then went right back to sleep. I don’t know what nightmare I had that drove me to get angry at my nightmares, I didn’t even have a plan to fight back. But that’s when it stopped, when I stopped being afraid of them.