I often wake up with a tense neck. I think in my case it's due to bruxism and sleeping in awkward positions, aswell as craning my neck a lot of the time when I look at the computer. I sometmes get "shocks" in the muscle, but I have a bad bite which can cause that - my teeth don't fit together very well at all, which can cause a lot of stress when I eat.

I used to think that the shock I got beneath my root canal filled tooth was due to the amalgam, but I've had it a couple of times since having the tooth extracted, so I don't know if that was it now. My aunt (not blood related) gets it aswell, and the dentist said it's not the fillings, which she was concerned about also.