An ASD person here: As child, my (ASD-like) mom got me worry dolls and guided relaxation audio that really helped. In college a professor stressed the importance of sleep and I continued my relaxation techniques; a therapist taught me imagery and lucid dreaming to imagine support to redirect nightmares. As an adult I would count down from 100 or at the worst times imagine a safe place (when awake I did EFT to handle the acute stress). My mom got me ear plugs that helps when I am agitated and every little sound is disturbing. Life is gentler now, but I still wake up when (moderately) stressed but have the discipline to go immediately back to sleep (sometimes I have to write some things down to get them out of mind), or if not, I get up for an hour, have a tea and then go back to sleep. For my elementary school aged ASD-like daughter, I lay with her as she falls asleep and she joins us in the morning for a bit before we wake up. She did sleep by herself all night for a while, but had a regression. All in good time. I have yet to teach her (in earnest) the techniques my ASD-like mom taught me, but I have them ready for when the time arises (and have floated a few by casually).