I was given reglan (metoclopramide) and benedryl by IV for a headache within minutes my RLS kicked in and then my hr went to 136 setting the alarm off. Why?

Reaction. May just have been a reaction to the medications. There should be no long lasting effects as the medicines get out of your body quickly. I would not call this a true allergy. I don't understand why you received Benadryl and Reglan (metoclopramide) for a headache as these are not "headache medicines".