We had the most amazing experience at Disney as well with our son, who has Aspergers. Some things over whelm him, as I'm sure you all know!

Like previous poster said -- my little man is a hopping, flapping, making noises and faces when he's excited, usually not a lot of reason to tell people, they can see it
Our first character meet and greet (not costumed, but live character) was Alladin and Jasmine. My kids were dressed just like them. My daughter was eating up the "you're going to meet a real prince and princess!!!" and my son just got... quieter.
Aladdin popped his head out to wave at my son and say Look at you, you're me! that's amazing! Aladdin was so happy to see another Aladdin.
As our turn got nearer, my son retreated, and then he RAN. I was taking pics of DD, Grandpa ran after DS -- and guess who else? Aladdin. Got up and left, followed my son, spoke quietly to him, and brought him back in. Jasmine said well Aladdin, I'm sure glad you came back in, because HE (points to big Aladdin) would be unbearable if he lost you -- We'd have had to run all over looking for you!"
Slowly, DS relaxed. And we got THE most amazing pictures EVER! And the most incredible memories!! My son was terrified about meeting a REAL prince and princess -- he got scared and got "stage fright" I guess. But Aladdin and Jasmine took the time with him. As it was our first day -- this literally could have made or broken our 10 day vacation. Honestly, that's when I knew, for sure, Disney was the happiest place on earth.
I'm all teary eyed just remembering! I wish I knew how to post a pic!