I think you should definitely go to your doctor as soon as possible. That "heavy hot ball in the stomach' feeling is highly unlikely to have come from low-carbing. It may very well be a virus but it should be checked out right away. If you notice in the bathroom that your stool (bowel movement) is very dark or black in color, go to emergency at the hospital. It could be an ulcer bleed. I hope that it is just a virus, but don't take chances.

Wishing you the best.

BarB