Hi, Welcome to Health care magic forum. You have got a swelling of the scrotum,all of a sudden,with out any pain. The hydrocele, is never with sudden on set. The other possibilities are inguinal hernia, or non specific swelling. I advise you to consult a surgeon for diagnosis and treatment.You may need to have an M.R.I. for diagnosis. If it is hydrocele,or hernia you may need to have a minor surgery. wishing for a quick and complete recovery. Thank you.