Lohan, star of film Mean Girls, was hospitalized last year for chest pain.
The doctors had diagnosed extreme fatigue, and had prescribed a few weeks of rest.
It seems that her very busy schedule, combined with family difficulties, (her parents are presently going through a divorce), would be the reason for this admittance to the hospital.
The 18 year old star is presently filming Just My Luck. Her working days can be 17 hours long.