A Pain in the Neck?

For two days now my neck has been getting more and more stiff and sore. I originally thought it was just the general tension 'crick' in the neck, but it kept getting worse. The unusual thing is that it is muscle soreness that seems to be isolated to two movements--not chin to chest or chin up, not ear to shoulder--but direct gaze over each shoulder both left and right side. This must be what it's like to have whiplash.

What gives? What could I have done to myself to cause this? I carried some pictures and posters at work on Monday, but that doesn't seem likely. Was I doing something crazy in my sleep (I have been known to sit up in bed laughing my head off)? Do I have some tragic illness that starts out this way? It was really starting to disturb me...but in a flash, I figured it out driving home from work tonight.

I'm thinking of buying a little house or a condo this summer and trying to get a sense of what the market is, so both Monday and Tuesday night I drove around my neighborhood until dark scoping out the homes in the area.

Drive, whip head left, whip head right....Drive, whip head left, whip head right....Drive, whip head left, whip head right. Repeat, ad nauseum.

If 'just browsing' for a home is this much of a pain in the neck, I think I might just sit tight in the apt for awhile...ouch!