I am a 21 year old White male, with sclerosing mediastinitis (the result of an unidentified mass in media-stynum of chest, perhaps caused histoplasmosis) and no other major health issues. Perhaps this has something to do with a strange symptom i have been having.

About 4 inches down from neck, and one inch to left off my sternum (near the top left area of my sternum?) I can feel a sort of bubbling or stirring within my chest, maybe 1.5 to 2 inches in. It feels like something sort of moving around , but there is no pain. it appears to occur randomly. I took my pulse while it occured earlier, and it remained constant and normal.

It is a very uncomfortable feeling that I have never had before. What could this be?