For the first question, if she had a stomach bug she can still shed the virus for up to 2 weeks after symptoms are gone. If this friend happens to take a bowel movement while at your party and doesn't wash her hands then she could be contagious. I think if she got drunk Saturday but didn't have a hangover and vomiting on Sunday then it was probably a virus. Most hangovers are clear by 24 hours after a drinking episode unless severe. For the friend with a weird cold, I've had this happen about half a year ago. I had such a bad cold that only got more severe as the days rolled by. She is probably nauseous from the mucus and weak immune system. She could have the flu if she has high fever, body aches and very weak. She doesn't sound like she has a stomach bug but you probably shouldn't come near her until she's feeling much better.