Chihuahua Manic Behavior

I have a six year old, 10 pound chi-dachshund mix named Hobbles. We adopted her from a shelter in March. She has mange on her back which makes us think that she may have suffered some neglect/malnutrition but she is very friendly so we have no reason to believe that she was ever physically abused. Hobbles has a strange behavior pattern we’ve noticed that I wanted to ask about. This occurs often when we put her in her crate, but occasionally with no clear antecedent whatsoever. She suddenly begins chasing her tail frantically, as if trying to attack herself, making aggressive noises. We call it her “manic attacks” because that’s the best way to describe it. Usually she does it once or twice for a few seconds at a time, but in severe cases it has occurred off and on for several minutes. What could this be and why do you think she does this?