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You seem to have 2 problems in your left upper limb.
1) Ulnar neuritis: The ulnar nerve
is one of the important nerves in your arm & hand; in fact it is known as the 'musicians nerve'. It is obviously getting compressed when you bend your elbow/ or sleep on it, as it runs behind the funny bone in your elbow. That is giving you the felling of heaviness in your fingers & also the pins & needles.
Usually needs surgery to free the ulnar nerve & bring it in front of the funny bone so it does'nt get stretched on bending the elbow.
2) Impingement Syndrome
: This is a condition when your rotator cuff
( set of 4 muscles in your shoulder) is getting squeezed in your shoulder under the acromion bone in certain positions of your arm.
Usually treatable by physiotherapy
to rotator cuff.
To start with you should go see the Orthopaedic surgeon
and he'll take it from there.
Dont worry, you can continue to enjoy playing the violin more than before once your neuritis is treated!
Dr. Mohan Thadi
MBBS, MS, DNB, FRCS(UK).