Sir sudden onset testicular pain is considered a urological emergency. I would strongly advise you to visit a nearby Urologist. There are three important and common reasons for this kind of pain. The first and most dangerous is Torsion of the Testis, in which the pain is severe and sudden. Usually this occurs because of lifting heavy objects or sexual activity. The second is infection of the Testis which usually develops slowly over days and is associated with burning in urine on many occasions. The third common cause is stone in the ureter whose pain can be referred to the testis. Other less dangerous causes are nerve entrapment, muscular strain etc