I don't think cats get separation anxiety like dogs do, because they are not a pack animal. They are a solitary animal and do just fine alone in their natural environment. However, a cat in a home is not in its natural environment. When it's awake, a cat needs physical excercise and mental stimulation. Cats alone at home get bored and unhappy because they have nothing to do. This is why often getting a companion cat is a good thing. If that's not an option, then be sure a cat left alone has plenty of toys accessible. Also, a window to look out of (a window shelf may be required). Also a cat tree and scratching posts so the cat can get some exercise. Even a radio on will help.