I'm no doctor, but doesn't vomit contain body fluids? If so, I would view this incident as the passenger coming in direct contact with the body fluid of the previous passenger due to negligence of the airline.

Perhaps they owe you a full medical check for contagious diseases. Maybe the passenger's sickness was something more than emotional?

If human vomit is in no way a bio hazard, then the compensation should be...I'll leave it to the experts.