The good news is you can't catch something that can cause vomiting by being around someone who is vomiting from a prescription reaction. It might even give you a chance to reduce your anxiety about vomiting. Maybe you should even be there if it happens! I became less anxious by being around people vomiting in college when I knew they were merely drunk and I couldn't catch anything.

Most likely your friend understands that people generally don't want to be around a vomiting person and isn't holding it against you personally.

Doug