Hi, I Have Been Taking Metronidazole 500 Mg For 3

Hi, I have been taking Metronidazole 500 mg for 3 days now for diverticulitis, and my neck has become very stiff and painful. I read on the Rx info sheet that I should get medical help right away if this side effect occurs, but I am snowed in by the current storm. Can you tell me how serious this side effect is, if it is lasting, and what will happen if I do not get immediate medical care?
Thanks