Mild pain in the penis after a nightfall (nocturnal emission) is usually not serious and is often due to temporary muscle or urethral irritation, semen passage, or increased sensitivity, especially if it happens occasionally. It typically settles on its own without specific treatment. You can manage it by staying well hydrated, maintaining good genital hygiene, avoiding tight clothing, and not worrying too much, as anxiety can increase awareness of discomfort. However, if the pain is frequent, severe, associated with burning during urination, discharge, swelling, or fever, it could indicate an infection such as Urethritis or another condition, and you should consult a doctor for proper evaluation and treatment.