It is generally due to stretching of nerve
due to abnormal posture while sleeping.
You can have restriction of arm with shoulderbinder and arm sling for 3 to 5 days. Along with this you can apply ice and pain killers. After 5 days you can start exerise and stimulation. If this does not help do ncv emg investigation and mri
of upper limb for brachial plexus
. Then consult brachial plexus surgeon.
Get well soon.