I think they know, but I'm not sure that they care. I was sick a lot this last winter, including a case of the flu that wouldn't go away. During that time, I stayed upstairs in bed most of the time, although I still had to work from home on my computer. My young cat, Ella, who was just over a year old, hardly left my bed long enough to eat and use the litter box. Whether she was being thoughtful and concerned, or simply lazy enough to find lying in bed all day to tempting, I don't know, but I'll give her the benefit of the doubt. I also have two twenty-five year old sisters, who have been with me since they were born. They are Cutie and Lydia. While I was in bed, Cutie would come up often, sometimes lying with me for a while, but she was more interested in trying to get me to get up so that I could come downstairs with her, since she prefers to hang out with me in my office. Was there concern there? Perhaps, but it was more of the "get your lazy butt out of bed and come downstairs where you belong" kind of concern. In other words, she noticed that I was still in bed but I don't think she realized that I was feeling badly. Lydia never once visited me.