might it have been too close to a radiator? or perhaps had a draught from an open door or window? both might make it suddenly " peaky"
Have you changed it's position?
It may not be beyond the bounds of possibility that it is vine weevil damage. We had them in the house for years, never knew where they came from or how they got in, assume it was from another houseplant. My daughter when she was little (she's 23 now!) used to tell me if she saw one and even made up a song about them! Lift your plant out of its pot and look to see if there are any grubs lurking among the roots. They are creamy with a brown head and curl into a 'c' shape. They like fleshy roots so the peace lily might be tempting. Overwatering might be another possibility, as that makes leaves wilt, so then you give it another drink.... though if you have kept it happy for years that seems less likely.
peace lilly like their roots to be compact, like an orchid,i did the same with mine so i repotted it again in a small pot, only realised when i read about it in a magazine