I have this same problem! I can't pinpoint the spot when I am sitting up, but the moment I lay down on my pillow I can feel the pain. I can't sleep on my back, which is fine for me since I am a side sleeper, but it is really strange. Did you ever find out what caused it? I haven't spoken to my doctor yet because it really just started a few months ago. Please let me know if you have heard anything else.

Don't be worried i think alot of us get it, I also have it. I beleive it's from stress and tension in your neck maybe causing this pain?