Summarize the following:
Even though cats aren't known for being the friendliest creatures, often preferring to be by themselves rather than constantly in owners' arms, they should not be constantly trying to get away from people. This can be a sign that they need a reduction in environmental stressors. If your cat consistently ducks out of the room or dodges behind furniture every time someone enters the room, you should try to figure out what's wrong. New cats may hide more than cats who are accustomed to their homes, so don't be alarmed if your new cat hides for a while after moving in. If you have a cat cohabitating with other pets, it should be easy to tell if aggression is a normal behavior or not. If your cat consistently snaps at or picks fights with animals it used to play happily with, the cat very well may be stressed. Your cat may be sick instead of stressed, so identify any stressors that could be triggering this behavior before heading to the vet. You are also probably attuned to how your cat interacts with other humans. If your cat used to be warm toward people, or even passively accepted their presence, and suddenly starts lashing out, you have a problem. Again, if you are mystified by this aggression, take stock of your home environment and identify any stressors. If there aren't any, the cat may be sick.
Notice when your cat isolates itself. Be concerned about aggression toward other animals. Address aggression toward people.