It could well be a reaction to your being away. Who took care of her while you were gone? Did she stay at home?

Cats, unlike horses, don't show they are ill until they are almost ready to drop. Cat guardians have to learn to be alert to small signs such as changes in behavior. Is she drinking more? Is she eating less? When you touch her, does she react more strongly when you touch certain parts of her body - such as the mouth area which could indicate dental problems? Does she play? Does she hide?