Neck Arthritis:

I didn't get whiplash from the car accident, not really, but my neck did get just enough worse that I was able to figure out a nagging problem: I had thought my sense of balance was degrading.

Actually that was not the case. Instead I found that if I tilted my head slightly forward and to the left, I fell asleep, causing my body to shift, so that I instantly woke up. I demonstrated this to my doctor.
"Doctor, When I tilt my head like this I fall asleep. What should I do?"
"Don't tilt your head like that!" (He really said that.)
But he explained I was pinching my carotid artery (SCAAARY!) and sent me off to the orthopedist.

When my orthopedist diagnosed my neck arthritis, he sent me across the hall to Physical Therapy so I could learn to do neck arthritis exercises. I returned ten minutes later to report that the Physical Therapy guy had said, "Well, there really aren't any neck arthritis exercises." Immensely irritated, my orthopedist found a worksheet and taught me a few strange exercises himself. I was suspicious that the Physical Therapy guy had been right until I noticed that I sneezed less often when I went outside into the sun.

All my life, going out into the bright sun has made me sneeze. Apparently that sneeze results from pinching nerves together in my neck, so that a visual stimulus triggers a nasal stimulus. (And there are lots more people like me who sneeze in the sun, so there!)