I got on a very crowded subway yesterday - it was quite warm in there. I was standing up but soon noticed I was VERY shaky and had to concentrate to keep from shaking. I also was very sweaty - soaking through my long sleeved shirt, undergarments and jeans. I could barely mount the stairs from the station and paused outside, leaning on something, taking some deep breaths. I barely made it to my apartment - I felt a little nauseous and shaky still - I lay down and fell promptly to sleep for over an hour (not my norm) - any ideas what this might be?