Sounds exactly like what juat happened two weeks ago to the 26 year old who manages the Music Store I teach at. Got light headed and went down banging his head on the counter. Given the same meds as you describe, told to quit drinking, straighten out his diet and hydrate a lot more. He told the doc that he doesn't drink or eat anything all day at the store. Closest thing they could tell him was they "think" it was dehydration, who knows.
Anyway take it easy and feel better soon. Good for you for the 911 call and not trying to pass it off.