I went on a long trip recently (2.5 weeks) during which time my cat, who is two years old, stayed with friends, who have a 9 month or so old kitten. I realise that it isn't ideal for cats to change environment, and that this could be a factor too, but I didn't have many options. Since my cat returned, she's been acting strange. I suspect that she misses the younger cat, whom she was apparently mothering and caring for during the holidays with my friends. She has been acting weird - a bit nervous, a bit less playful, and even tail-chasing here and there (which I had never seen before). We recently went to the vet as she had been breathing heavily, which itself may have been stress-related (missing the cat, or changing environment). thoughts?