Likely a fictitious disease: An unhealthy (presumably fatal) extremely large persistent erection.
Mentioned as the cause of death of Henry Flanken who possessed a genie. As Mulder describes it, "Schwing. On April 4, 1978, he was admitted to Gateway Memorial Hospital with an extreme priapic condition. Apparently, he was quite the specimen. They had to raise the door frame in order to wheel him into his hospital room."