Driving while sleepy is always dangerous. So it stands to reason that drivers with sleeping disorders might be more prone to accidents.

According to a study published in the journal Thorax, that’s true for people with obstructive sleep apnea [APP-nee-uh] or hypopnea [high-POPP-nee-uh]. Those are conditions that restrict airflow to the lungs. They can result in daytime sleepiness.

The study involved almost eight-hundred adults who’d been referred to a clinic for suspected apnea or hypopnea. They were evaluated for sleep disorders and classified based on the degree of breathing disturbance they experienced. The researchers also checked motor vehicle accident records on each patient for the past three years.

An equal number of control subjects were recruited for the study, and their accident records were examined. Overall, patients crashed twice as often as controls. The disparity between the two groups was greatest for the most serious accidents, the ones involving personal injury. Patients with substantial breathing disturbance were three to five times as likely to be involved in those crashes, compared with control subjects.

The researchers also found there was little correlation between the degree of daytime sleepiness patients reported, and the number of accidents they had. So it may be that drivers with sleep disorders can feel more alert than they really are. Or perhaps their alertness levels can change rapidly.

Whatever the case, one thing’s for sure… if you’re habitually tired, see a doctor. Because bed is the only safe place to crash.