I recently struggled with neck pain -- woke up one morning recently with the whole side of my neck having this burning sensation, scared the heck out of me for awhile there -- so I know your struggle, albeit on a far smaller scale. Honestly sounds like you know the root of the issue, and there's absolutely no reason to believe this tension is all of a sudden going to overtake you and cause some serious damage at the drop of a hat. If anything, it sounds like you're taking all the necessary steps to FIX the issue (going to doctor, etc.) Also, as you probably know, the neck is always a go-to region for accumulated stress, and that can't be helping your situation at all (nor your obsessing over the injury).
All of this aside, although I'm no doctor, it doesn't seem like you have any reason to be "terrified." Upset that you neck was messed up by exercising? Sure! But terrified? Certainly not. Your neck injury will not lead to some head injury, or anything of the sort. Take some ibuprofen, try to relax, and talk to your doc tomorrow. Neck's can be pesky, but I'm sure you'll be better in no time.