Starting maybe two months ago, my gregarious and affectionate black cat, M. Gastón, began spending more and more time away from the house. I would let him out, and he wouldn't come back until the next day. Then he'd stay gone for two days, then three. Sometimes I would see him sleeping on a neighbor's porch, or wandering through a front yard across the street. He's been gone four or five days this time.
In the meantime, my grumpy old ex-cat, Rollo, has come back home (with some encouragement from me), and is sleeping on the bed with me this evening. He's been living with neighbors for more than a year, and I think he left because he didn't like Gastón. He's OK with being here as long as he's the only cat.
I wonder if this has anything to do with one or both cats sensing my illness. Probably just coincidence.