I was helping a friend (actually, it was my water aerobics instructor) move out of her apartment and into the house several blocks away she'd just bought with her husband. I helped load everything into a U-Haul, drove over to the house, and helped unload it - and apparently sweated away a good bit of my body's moisture without sufficiently replenishing it. The next morning, my inner ear was all messed up, such that every time I moved my head it felt like the world was spinning. It took a day or so to get everything back into balance.
Johnathan