I have learned at the clinic I was treated at that "toxins" of any kind- bacterial, viral, fungal or environmental can settle in the muslces of the neck and spine. That is why so many people with Lyme have a stiff neck and it normally improves with treatment. Have your parents had any work done, (painting etc) recently at their home? Check anything that can cause fumes, etc. I have a friend that suffers from severe stiff neck whenever around propane. (an example) I am the same way around any mold, no matter how slight the exposure. D