My mother has had this 17 year old male cat since he was less than a year old. This summer she was diagnosed with cancer, had the recommended operation and is currently taking chemo. She was away from home about 2 months and finally got home a few weeks ago. The cat used to sleep on her bed at night, came to her to get petted and groomed, etc. Now he is quite distant to her. When I put him on the bed with her, he just walks off. Can cats tell when somebody is quite sick? Why is he avoiding her so much?