I don't know why but I experienced the same thing when I was sick with the stomach flu. They got MUCH worse and my HR increased a lot, too.
theres alot of reasons, it has to do with the bodies physiological response to nausea and vomitting, it could be dehydration, fever, a bunch of things.. But it is normal.. I hope you get over your flu soon!! I already had a bout with it this year (and i was on vacation! :( Not fun! feel better
that your potassium level drops with dehydration (from vomitting and diarrhea) and your body needs a normal level of potassium and sodium which is finely balanced in order to function and have your heart beat normally. There is a direct correlation between a low potassium level and palpitations increasing. If you already are predisposed to palps, then they will inevitably get worse until your electrolytes are back in balance. You can try to prevent this by taking a few mls of gatorade or similar every few minutes while you are sick.
Hope this helps and you are back to feeling great soon.
Fiona