I didn't know he;d been in hospital, my cousin swore her sons (NT) was always bad after GA's - she used to use homeopathy.
Anyway meltdowns- I find staying there to try and prevent harm, but switching off emotionally and not trying to stop it is the way to go. So if he's headbutting something I might say "no headbutting" and put my hand between his head and the surface, if he;s biting himself then "hands down". I also try to sidle in and distract, although that often takes a long time to work.
At times when you have to move them, I think there is very little that can be done. I sometimes have this outside and it is very difficult. I really want to organise some parental handling training- will of course let you know if/when we do.