I was prescribed melatonin when I was 11. In the UK it is only available via prescription (source on that: https://www.simpleonlinepharmacy.co.uk/health-advice/sleep/melatonin/why-is-melatonin-banned-in-the-uk/#article )
My sleep schedule was haywire (hormones + emerging gender dysphoria did not help) but melatonin really helped me. I also think it helped my anxiety a bit? I’m not sure if that was just bc I was sleeping better but I have terrible social anxiety and it seemed to take the edge off it. anyone else? :)
Not autistic.
Melatonin should help you fall asleep. It works great for me at 3mg. It will not really keep you asleep and I’ve never heard of it reducing anxiety.
Antihistamines however(hydroxyzine, promethazine… and more), they’re good at all of this. Falling asleep even, but not to the same effect as melatonin. Downside is the length of effect, you usually wake up being tired for a few more hours.
There are brands that sell melatonine that will start working after some time. My son gets a blend of fast and slow release melatonin, as he had the problem you describe: fall asleep somewhat normally and be wide awake in the middle of the night.