Hello! I m sorry to hear that you are experiencing such symptoms. Random heart beats in a 21 year old can be caused by many things, I ll adress the likely candidates. Is there pain associated with these random heart beats? Have you started any new medications recently? If there is pain I would be concerned about something involving the Chest Tube insertion/pneumothorax. If not there are other possibilities! #1 could be caffeine, alcohol and or any toxin/medication use that your body does not respond well to. Another could be blood sugar. If your body is not obtaining the nutrients it wants sometimes it will respond with the shaking and fast heartbeat you describe! I suggest you try to eat smaller meals, but more often, hydrate, and assess how much caffeine, alcohol and alternative medications you may be taking (Steroids, anything other than multivitamins). If you change this around and see no improvement, or experience chest pain, certainly have yourself checked out by a physician. I hope this helps!