So I have this weird sensation of chest pressure when sitting or laying flat on my back. I've been to my doctor and had various tests done (stress test, 24 hour heart monitor, EKG, ultrasound) and everything comes back normal. I do suffer from mild acid reflux and a small hiatal hernia. I'm an active 55 year old male and exercise 5-6 times a week, engaging in high intensity interval training 3-4 days a week and never suffer chest pains or difficulty breathing. The pressure only occurs when laying flat on my back and at times it becomes overwhelming. There are occasions where I can lay on my back and not experience the pressure but that does not happen very often. Does anyone out there have similar experiences under similar situations?? Please let me know your findings if you do-I am going crazy over this!!!!