Pain in the neck

Since returning from Birmingham I've been suffering from a painful stiff neck. This is a problem at least a decade in duration but for the last few years it has been a minor, infrequent irritation on the whole. Taking care with sitting and regular massages seems to keep it in check - mostly. I've no idea what set it off this time; thin pillow, heavy rucsac, cold air, all of these plus swimming? Who knows? Anyway, it's not pleasant although the only impact it seems to have on exercise is making it uncomfortable to lie down for floor exercises.