You probably got an old fashion BB'ers niacin (vitamin B3) flush. Faster heart rate, itching, usually in the upper body, neck and head and flushed skin. Niacin is found in whole yeast products, Too much, at one time give these affects. Also depends if the yeast is poorly made and not balanced correctly. Usually last about 10 to 15 minutes in all. But you think your having the big one and about to die.
Niacinamide (again vitamin B3) is buffered form of niacin without all the side effects of the flush. In high school we use to take niacid tablets, with beer, just because we could. Cheap thrill when your 14-15 years old.