Hi. Thanks for your query. Noted your history of feeling a little pulsation under the left rib cage, got curious found out on internet as ulcer. It must not be as it is painless and you noticed one night when lying down. The most probable causes of such swelling is: Costochondritis of the ribs. Old fracture that has healed May be a lipoma or a sebaceous cysts as it is painless. I would advise you the following: Get this examined by a General Surgeon. If this turns out to be cyst or lipoma, it is better to get this removed as it may increase later on and cause problems later on. If this is something else, your Doctor would helps you with the diagnosis and proper treatment as the