Air pocket like lump 1.5 inches below sternum. lost weight via workout. seen when lying down or flex abs. no pain. no other symptoms. male. 25yo?

Epigastric hernia or: Greetings Sir, Rectus abdominis diastasis is separation of the rectus abdominis muscles that can occur causing a protrusion when flexing the abs or doing sit-ups. This also may be an epigastric hernia. Either can be diagnosed based on a simple physical examination by a physician but additional testing such as an ultrasound may be needed. Best regards..