When It Comes To So Many People...It's my problem, too.
1) In classroom where we are about 30 people and I must spend a day with them... I come home absolutely drained. I fall asleep at least for 1 hour.
2) in shopping malls, I get headache after 20-30 min spent there. Ugh...
I don't like to be around too many people because of my own mental ( ! ) and also physical state.