A total of 55 students at Michigan’s Olivet College were hospitalized in recent days for a mysterious illness that displayed symptoms including light-headedness, nausea, and dizziness. The students were hospitalized and tested for carbon monoxide poisoning but have since been releaed. Every building on campus has also been tested for high levels of carbon monoxide, but none tested positive. It is unclear what is causing the illness but the Lansing State Journal reports that at least 25 of the hospitalized students live in a men’s dorm called Blair Hall. The school temporarily closed the dorm but fire department officials have since said that carbon monoxide is not to blame for the sickness.