Right Mumsnet am I going crazy or is this a possibility?
I've never been an exercise freak, but try to go to a class or two a week just to try and keep the flab at bay because I'm partial to nice food and the odd drink here and there. I mainly do spin classes or something like Zumba.
On the odd occasion I've pushed the intensity a bit, and done something like a run on the treadmill and maybe got a bit hotter and sweatier than usual I sometimes go all blotchy and break out in a kind of hives situation 
There has been two occasions recently, one including this afternoon where following a run I've literally come out in a rash, had to dash to the loo and I swear today my tounge was actually tingling, no swelling though. Genuinely felt rough for a good hour or so afterwards and have taken an anti-histamine. I'm starting to actually panic I've got some sort of allergy to higher intensity exercise
Google tells me it's possible but extremely rare.
Has anyone ever heard of this? It's really put me off exercising if I'm honest! Will obviously be cautious and making a Drs appointment but am I going mad?