As a PP has mentioned Melatonin is often prescribed for children with SEN especially autism.
Lots of children I worked with were on it and many parents swore by it. It is usually intended to help children get into a sleep routine.
I bought a Snoozeband to help me to get to sleep and when waking in the night. You may have already tried? I can highly recommend.
stephen king for a 13 year old?
do you have plasterboard on your walls?
