As MrsD would always remind me, if you're going to have your B12 tested make sure you don't take it for a few days before so you'll get a true reading.

Were the crabs spicy as well as salty? Spicy food is a trigger for many of the people in this group. That, caffeine and alcohol.

The only other thing I can add is imo age is a factor. Looking at the list of hobbies you could have something going on in your spine. Or not. My SFN came out of nowhere and I haven't been able to get a dx. I have to think it's been there waiting in the wings. As I aged it just became harder for my body to hide it.