Thanks for your query.
Hard painful knot to the left of spine under back of skull.
Certainly yes, you should be concerned.
This is not normal. Can be due to a Lipoma, Sebaceous cyst, muscle mass and so on.
I think, you should consult a Surgeon for clinical evaluation, investigations like ultrasonography, FNAC, MRI, excision and so on.
Get this done ASAP,
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