When one strains to increase the flow of urine, it stimulates the vagus nerve (usually more pronounced in elderly men with large prostates). The vagus nerve stimulus causes slowing down of the heart (bradycardia) and a drop in blood pressure. The heart cannot perform effectively as a pump because insufficient blood comes to it. It can be associated with a very rare tumour known as a paraprostatic pheochromocytoma within the urinary bladder. <!--
Micturition syncope
Heat syncope
Reflex syncope
Laughter-induced syncope
Post-micturition convulsion syndrome
Vasoplegic syndrome
Abdominal aura
Acathexis