Yes, I got really sick just before Jollywood Nights last year and had to go to first aid. I had to check in and out. I did stop by Guest Services on the way out because I didn't even make it to the beginning of the party. They were kind enough to refund our money. They escorted us out of the park; I assumed they wanted to verify we weren't using the tickets, which was fine with me.
ETA: There was not another night we could have gone to Jollywood Nights during our trip.