Defecation syncope: The temporary loss of consciousness (syncope) upon defecating (having a bowel movement). Syncope is the temporary loss of consciousness or, in plain English, fainting. The situations that trigger this reaction are diverse and include having blood drawn, straining while urinating (micturition syncope) or defecating, coughing or swallowing. The reaction also can be due to the emotional stress of fear or pain.

Under these conditions, people often become pale and feel nauseated, sweaty, and weak just before they lose consciousness.

Situational syncope is caused by a reflex of the involuntary nervous system called the vasovagal reaction. The vasovagal reaction leads the heart to slow down (bradycardia) and, at the same time, it leads the nerves to the blood vessels in the legs to permit those vessels to dilate (widen). The result is that the heart puts out less blood, the blood pressure drops, and what blood is circulating tends to go into the legs rather than to the head. The brain is then deprived of oxygen, and the fainting episode occurs.

The vasovagal reaction is also called a vasovagal attack. And situational syncope is also called vasovagal syncope, vasodepressor syncope, and Gower syndrome after Sir William Richard Gower (1845-1915), a famous English neurologist whose name is also associated with a sign, a solution, another syndrome, and a tract in the central nervous system.