I had a panic attack in the crowd at a gig last summer, was a bit of a nightmare getting myself out (it was the Paul McCartney headline set at Glastonbury so a huge crowd of perhaps 100k). Sometimes these things can just happen out of the blue, almost without reason, it wasn't like it was a rowdy crowd or anything, just bang! panic attack! I managed to get myself out of the back of the crowd and to somewhere quiet to ride it out.