Hello,
It may be related to nerve impingement (pinched nerve), which can originate in the neck (cervical spine). This condition called “Brachial Neuritis”, or “Brachial Neuralgia”, is due to the involvement of the group of nerves exiting from the spinal vertebrae, called the “Brachial Plexus”.
Secondly,it can be due to spasticity of the trapezius and underlying smaller muscles. The spasticity of the muscles can be brought on by overuse or trauma to the muscle.
Lastly your cardiac status also needs to be evaluated.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I would definitely seek medical attention as soon as possible.