Awesome job with telling the hospital exactly what YOUR kid needs!!!! AWESOME news
Besides ADHD tests, what others will they give him? He should have "full" psychological exam, that consists of appx 4 hours. In addition while he is on the unit, they doctors should be noting any cycling of moods, or psychological abnormalities, that help them reach a better conclusion in medicating them.
You are on the right track with him....don't let them release him until you have everything you need. Follow up care, a Dr, the proper medications, etc.
As for him missing Halloween - it might be that you are being more nostalgic than he is sad about missing the holiday? You know? Not that I am judging - cause I have those same feelings even today - but it helps to keep it all in perspective. He is probably not as upset as you are.....and is watching a scary movie and eating candy on the unit.....
HUGS :<