We're at a family friend's house so my brother and I had to share a mattress. I have a huge fear of getting sick. I couldn't sleep because I was afraid he'd be sick, and then he gets up, goes to the bathroom, and vomits. Now I went down to the basement to stay there. Will this make me sick? Do I already have the illness? Tomorrow I have to ride home with him in the car, will that make me sick?
You've already been exposed to anything he was incubating, so stop worrying and wait and see if you get sick. It could have simply been food poisoning, which isn't contagious. In the meantime, wash your hands with soap and hot water frequently.