If you're doing internet research about catatonia, particularly milder forms, you may also want to try some of these terms:
Childhood catatonia, autism and psychosis past and present: is there an ‘iron triangle’? - E. Shorter and L. E. Wachtel
An academic article on the possible relationship between autism, catatonia and childhood psychosis, looking at the history of these diagnoses.
Catatonia and catatonia-type breakdown in autism - Dr. Amitta Shah
An accessible article about autistic catatonia.
Autism and catatonia - our story
A personal story