I found a hard lump on the back of my neck, smaller than a marble. It's not squishy and doesn't move around under the skin. Feels like its well beneath the skin. I just noticed it today so it hasn't been there very long. This sorta freaked me out and I'm wondering if it could be something harmless, or if I should get this checked out asap. And would the ER do a biopsy or whatever of it or would I need to go to my regular doctor?