I would say, guilt is primarily a state of consciousness. Did you come across the scale of consciousness? On the scale, it dwells on the low side and is the second worst state a person can be in. There is a numbness for emotions coming with it, a disconnection to the own emotions, which results in a strong sense of separation. It's hard to say, but I would name it an emotion, or at least a replacement for an emotion.
RE: Emotional Healing: Having Guilt Does NOT Mean You Have Done Something Wrong (Or Are Wrong) (Other than having listened to blame!)