On the second floor of my house next to the stairs, there's a short stretch of hall with a closet in the wall and a window at its end. It's made narrower by a shelving unit on wheels and cluttered with 2 rolled up rugs, boxes, laundry baskets, as well as fabrics and curtains slung over the railing. I was just about to move the laundry baskets and crawl over the rest to get a box of mine in search of a lost letter from Katharine Hepburn when I noticed the ceiling above has a distinct sag. I've always had a great sense of level and the trap door for the attic is definitely sloping down away from the wall; it levels out again where the track lighting is above the stairs.
I have a feeling it's always been that way (at least since the first time I moved here 17 years ago), and I'm disturbed just as much by the fact I didn't notice it until now, or that I'd forgotten I'd noticed it, as I am by the slope itself.