Epileptic individuals who sleep on their stomach may be at increased risk of death, according to a new study.

Among 253 instances of sudden unexplained death in epilepsy (SUDEP) in which body position was documented, nearly three-quarters of the victims — 73.3% (95% CI 65.7%-80.9%) — were found in a prone position, according to James X. Tao, MD, PhD, of the University of Chicago, and colleagues.

“In addition, the prone position was reported in all 11 cases of video-EEG-monitored SUDEP,” the researchers noted in their report, published online in Neurology.