So, you have a very old house, that has creaked and groaned for decades. Stands to reason that without reasonable maintenance, like plaster repairs and painting when necessary, things deteriorate.
Big humidity and temperature swings can also cause problems, as the wood lath and frame work move, swell, and shrink. It's all a part of that house living for 120 years. I'm betting you also have substantial cracking under the wall paper.
The only two cures I know of is repair and paint, (extensive) or have them resurfaced. You could sell the huge thing and move into something smaller and newer, without the age problems.
Yeah I've got O.C.D. Old, cranky, and dangerous.
Everything will kill you, so choose something fun!