It happens whenever I have strenuous exercise for an extended duration; for example, when weight lifting I'll start to run out of breath on the 3rd set, by the 4th set I'll be completely out of breath and have the beginnings of a massive headache/dizziness even if I wait a solid 3-4 minute rest period before continuing. Checking my heart rate/blood pressure at that point in time shows low blood pressure and a skyrocketing heart rate.
I don't have any food allergies that I know of and I'm normally working out in a gym/studio.
Thanks to all for the well wishes, it's frustrating to have a good workout routine then have something stop your progress.