when you went to one of the appartements of the complex, you didn't expected to find the culprit behind what you took for night terrors and paranoia... And for 'it' to be infact a 'she' with such an appearance, affection toward you..... and the desire to turn you into one of her kind (said others who you met all around the appartement)

You refused that 'remaking' proposition, much to her dismay, but knowing she was certainly going to come back in the middle of the night to do her usual 'sleep paralisis demon' behavior while you slept, you proposed to her to come to your place instead, and needless to say she jumped on the occasion

She doesn't really roam around that much, staying either in your residence or back at the place she was remade with the others in her case

So when you get back to your place, almost out of muscles memory, you turn off the lights of your appartement, knowing that she must be near and most likely waiting to greet you back home.....And bingo, Once the lights got turned off, Spine's body, until then invisible, gradually became more material, so that you could finally see her sitting on the couch, her skinless form resting on the soft furniture in a position that is mocking a cat loafing