For the last 2 days my cat has had very runny movements, and today seems to have a high temperature, slightly irregular breathing, and is occasionally vomiting up a frothy white liquid. Does this sound like just a sick cat who just needs a day or two to get better, or does it sound more serious? She does not appear to be in excruciating pain or anything, but she is less active than usual, although not to an extreme degree. We just brought a new kitten into the house, could this just be stress?