Sudden pain in the shoulder and upper arm could be due to many reasons. I have few questions like How long do you have this pain, Do you have neck pain, Which side of the shoulder, Is the pain radiating from neck, Which activity increases your pain and which activity decreases your pain? Are you diabetic?
You can apply hot water fomentation on your shoulder and upper arm. This could be done for 10-15min twice a day. You can use Volini spray or gel provided you are not allergic.
Next Steps
If the pain persists for more than 3days after these treatment you have to consult a Physician or Physiotherapist or Orthopaedist for further evaluation and treatment.
Health Tips
Note: If you are diabetic then ensure that you don't place the hot water bag for long time in the same spot to avoid burns.