The most extreme example that I had with mine was the day that I learned that a dear friend of ours died in a car accident overnight. His family lived in another state, so DH and I spent the day away from home, taking care of things on behalf of the family until they could get here. We were both highly stressed that day, and only popped in and out of the house a couple of times throughout the day. When we finally got home about 1 AM, I noticed that my Muddy was walking around growling at the other cats (he's normally the sweetest cat in the house), and then straining in the litter box. While he had chronic urinary issues, our stress caused him to block and I had to rush him to the ER in the middle of the night. When the vet at the ER asked when it started, I told them that I had no idea because I was gone most of the day due to our friends accident. They gave me the knowing look and told me they've seen this before - the people get stressed and pushes a cats medical problem over the edge. Poor Muddy had to stay in the ER on a catheter for a couple of days that time, and oh boy, what a hard lesson that was for all of us. Note to self: if you have a cat that has a stress induced illness, hide your stress from them.