How soon can they take out the tonsils & adenoids? I would be very wary of giving him anything to help him sleep, while he has sleep apnoea (as you describe form the sleep study).
A classmate of difficult child 3's (after school class) sounds very much like your son. This girl has bad sleep apnoea, so bad her mother can't get her to school. The kid is totally manic when awake, especially at night. She won't go to sleep until after midnight then in the morning the girl can't even be roused to go to school (the truant officer was invited in by the mother, rogether they put the girl into the previous night's bath, now cold. The girl was fully clothed and still didn't wake).
The thing is, from what we can work out with this girl - to sleep, it feels like suffocating. Her dreams are coloured by sensations of suffocation, she has nightmares because of it, and so she is afraid to go to sleep.
The girl has developed a problem with how her rib cage is forming, because of her breathing problems.
She has finally had her tonsils & adenoids out, now they're finding more success with things like melatonin. Before, she was fighting any natural tendency to sleep (and you know how kids can get manic when they're overtired). If they tried to sedate her, she still wouldn't sleep (it was like trying to tranquilise an elephant, her mother said). But when she finally did get to sleep, the girl was even more difficult to rouse. The girl now has to learn how to go to sleep, and that it's OK now, she is safe. That is taking time.
ON the subject of vomiting - difficult child 3's school accused him of making himself vomit. We finally worked out that it was severe anxiety. He also reacts to certain medications.
In my case - if I take a vitamin preparation containing iron, it comes back up with little warning, within minutes. Even if I drink water that has been in pipes contaminated with iron or copper, I throw up. It began with vitamins and each subsequent exposure the vomiting happened faster. Also, vitamin preparations are often naturally coloured. Iron salts are often yellow or orange (sometimes red) and Vitamin A is red. Sometimes there is artificial colouring in there as well.
So the vomiting could be a reaction to one of the components of what he is taking, or it could be an anxiety reaction.
Sounds like you have a problem here, but if it's just sleepl apnoea plus restless legs, it could improve a lot ofter the operation. Fingers crossed.
Marg