She was having a stroke. Doctors later concluded the stroke probably was due to several related factors, including birth control pills, a venous blood clot, sexual intercourse and a heart defect.

Doctors at Loyola University Medical Center describe the unusual case in the Journal of Stroke and Cerebrovascular Disease.

Birth control pills slightly increase the risk of blood clots. Doctors believe a small clot formed in one of the veins in her thigh, broke loose and traveled to the right atrium (the heart's upper right pumping chamber). Normally in such cases, the clot will get pumped out of the right atrium and travel to the lungs, where it may harmlessly dissolve.

In this case, there was a hole in a wall of the heart separating the right atrium from the left atrium. Pressure changes in the heart, triggered by sexual intercourse, enabled the clot to travel through the hole from the right atrium to the left atrium. From there, the clot traveled up to the brain. It lodged in a narrow blood vessel, blocking blood flow to an area of the brain that controls movements on the left side of the body, said Dr. Jose Biller, co-author of the report and chairman of the Department of Neurology at Loyola University Chicago Stritch School of Medicine.