Now maybe its all a bit unfair at this stage to suggest the following but after a quick google on 'mass hysteria' brought up this link to a reuters article:
http://www.healtoronto.com/hysteria.html
other similar links are produced.
quick precis
"In a study of a November, 1998, outbreak of illness at Warren County High, School in McMinnville, Tenn., Timothy Jones of the Tennessee Department of Health and his team found no evidence of any medical or environmental cause for the sickness, which affected about 186 people in two incidents.
The first incident started when a teacher at the school reported a "gasoline-like" odour in her classroom. Shortly thereafter she became sick. Other students also got sick and were taken to the hospital. The school was then closed.
Symptoms included headache, dizziness, nausea, drowsiness, vomiting and many others. They were reported by students all around the school.
A second rash of cases occurred a week later, a day after the school reopened, again resulting in the closing of the facility. After the second incident, an extensive environmental and epidemiological investigation was launched.
While Dr. Jones and his team emphasized that the symptoms reported by victims were no doubt real, they still said they were probably a case of mass hysteria.