What thoughts are going through a person's head during catatonic stupor?

What is going on in a person's head during a catatonic stupor (as a symptom of schizophrenia)? Are they completely unaware of their surroundings, as if asleep, or are they consciously processing everything but just failing to respond? Do they want to respond but just can't, or are they indifferent - almost as if hypnotized?