nothing. absolutely nothing that I took notice of. I might have had a headache, I don't remember. But headaches are kind of a part of my life, it's not unusual for me to get one so if I had I wouldn't have thought anything was wrong. Literally the first sign was fainting. It was very strange. I kept asking the nurse and doctor, really?  I'm dehydrated and it caused me to faint? Really?    And they were bewildered that I had no other signs either. But when I mentioned I had the stomach issue the prior day he just nodded and said, yep.