I've had spells of horrible neck weakness. It is one of the most uncomfortable symptoms there is because you truly need to use your neck muscles for EVERYTHING. I've had summers where I was unable to work in the garden due to it, and it was #2 in my reasons of why I had to give up my career.

One thing about it, though, is that the neck weakness, at least in my case, tended to get worse for a few weeks and then return to baseline (which is weak but not AS weak). Hopefully yours will ease up for you soon.