I think I'm becoming hypersensitive to caffeine. The other day I drank one mug of decaf green tea and a mug of decaf coffee. The amount of caffeine in those was negligable, to say the least. But 15 minutes later I had a headache. Not a full-on migraine, mind you, but a headache.
Then yesterday I ate a Snickers bar. Yes, chocolate has caffeine. It gave me a headache.