An unexplained, self-limiting illness characterized by nonspecific symptoms in persons in a social setting such as a school, workplace, church, or military group. The onset is usually rapid and may occur after an unusual or peculiar odor is detected. Symptoms may include dizziness, weakness, headache, abdominal pain, rash, itching, blurred vision, nausea and vomiting, and fainting. There are no laboratory studies to confirm an etiologic agent. Resolution of the mass illness may occur when those affected are reassured that it is not due to a toxic substance or disease.