Priapism
Priapism is usually a painful erection of the penis that lasts longer than four hours and is not, or only insufficiently, related to sexual arousal. It is a medical emergency because, if left untreated, it can cause permanent tissue damage and impair erectile function.
Possible causes include medications, blood disorders, injuries, or unknown triggers. If priapism is suspected, immediate medical attention is required; home remedies, waiting it out, or further sexual stimulation are not appropriate and may worsen the situation.