Hi James, I can only give you some general information. You really should see a doctor or a nurse at a health center to rule out any thing serious. Besides the possibility of a hernia it could also be a swollen
(gland). Have you been sick lately, or if its a mild hernia, have you lifted, pulled anything heavy? Even wrestling and rough play (football) can cause it too.
Hernia's are bulging sections in a muscle or blood vessel. An inguinal hernia is a soft lump
or near the belly button that disappears when you press on it or gets bigger when you cough. It may also hurt when you cough. See below web sight, for more info. in case it is a hernia. It shows what the treatment consists of and the sooner its treated the better the outcome! Thats about all I can offer. Hope this helps you.
Two possibilities are there.Firstly it can be a swollen lymph node. . Lymphadenopathy (swollen lymph nodes) is usually caused by a viral or bacterial infection. Other causes include allergic reactions, arthritis, cancer, metabolic diseases, and an overactive thyroid (hyperthyroidism).
Second possibility is of inguinal hernia although its chances are less because it is a painless swelling which disappears on lying down.However for the confirmation of a diagnosis pls consult a general surgeon.
Hope it helps. Take care and pls do keep me posted on how you are doing or if you have any additional queries.