I have been sick with watery diareha for 3 days i went to store today and started breaking into cold sweats and was light headed is that from dehydrat?

Could be: It sounds as if you were having a vagal episode of some sort which simply means that your blood pressure may have bone down, perhaps from being on your feet for a while and being in a volume depleted state. It could be that you were also hypoglycemic (low blood sugar) if you haven't been eating your normal daily routine due to the diarrhea. You should check with your doctor as soon as possible.