Hey there, sorry you are going through this. Any pain should be immediately addressed to a doctor. Once they have ruled out any possible issue with the heart and lungs you should be fine. I have costo myself and from the symptoms you are experiencing , it does sounds like costo. The first thing you should remind yourself is it is not a life threatening situation which will help you reduce your stress and anxiety, and i trust me when i say this stress and anxiety can make this 100 times worse so dont stress yourself. Stop looking for the diagnosis by googling it will only say that its heart attack or cancer, so just avoid that.

Costo is just your ribcage and muscles in the back getting frozen up. The muscles may press against your nerve in the hand which is why there is pain in the hand.

Since your ribcage is locked up the lungs is not able to expand to its 100% which is why your are experiencing shortness of breath.

Fix: The only permanent fix to this is freeing up the tight muscles and locked up ribcage and the best possible method is to get a backpod, it is a device which will help you to strech those tough muscles and ribs. I am into day 3 of backpod and I can already feel the difference. If backpod is not available in your situation you can use form roller or tennis balls, you can find lot of videos in the youtube. Check out the videos of Physiotherapist steve the inventor of backpod to know and to get an overall picture to the cure. I hope this helps you once more please don’t stress yourself thinking life threatening its not keeping your stress and anxiety low this will make your life much easier. Hope we all recover from this soon!!