Hello Good Evening,
This seems to a muscles pull by abnormal position while sleep.
In body in a particular position remains for a long time then there will be a fatigue
of muscles can occurred and pain, stiffness
and even swelling may occur due edema.
So you should not bother to heavy and take some muscle relaxant
, pain killer and anti-inflammatory medications as per prescription of your GP.
Pain will subside gradually, as will see improvement day by day.
There is nothing harm to do ECG again to rule out any cardiac problem, and it must be done in any atypical chest pain
So please go for a ECG then further management.
Dr. Naresh Jain.