Working out what might be wrong and how to fix it.

Environment-

Too hot/cold
Room is too light/dark
Too noisy/not noisy enough/wrong noise
Other things/people (partner/family/house mates/pets)

Solutions for environment-

Use a fan, heater or heated/cooling blanket
Use blackout blinds or a night light
Earplugs (amazon sell mouldable ones that are supposed to be very comfortable) music/audio book/comfort show etc.

Sensory-

Wrong smell in the room
Bedding feels wrong/overwhelming
Clothing; itchy labels/ uncomfortable fabric
Too hot/cold
Sleep/general anxiety causing physiological symptoms that cause sensory issues
Feeling poorly, headache, body ache, tooth ache etc
Wrong smell in the room

Solutions for sensory-

A room diffuser with a comforting scent (lavender is good for sleep)
Find the best bedding for you (I prefer 100% cotton or bamboo bedding as its softer on my skin)
Change of PJ's ready if needed/cut out labels carefully
Fan/heater or heated/cooling blanket
Weighted blanket (I have one and it is the best purchase I've ever made for my sleep, it may be good to seek medical advice)
Take painkillers as per instructions, have a bath

One thing I've found in my research is that most of the information isn't very autism specific and thus you need to pick and choose what works for you. Its a case of trial and error.