Catatonic schizophrenia is a severe subtype of schizophrenia characterized by extreme fluctuations in movement, where a person may exhibit either complete stillness or extreme hyperactivity, often accompanied by a lack of speech, staring, and repetitive behaviors, essentially disrupting their motor function significantly; it’s considered an outdated term as “catatonia” is now seen as a symptom that can occur within schizophrenia, not a separate subtype.