Information on catatonia and catatonia-like states for autistic individuals, who are more likely to suffer from an intermittent form of catatonia than one that is acute or malignant. A description of catatonia from the DSM-5 "Catatonic behavior is a marked decrease in reactivity to the environment. This ranges from resistance to instructions (negativism); to maintaining a rigid, inappropriate or bizarre posture; to a complete lack of verbal and motor responses (mutism and stupor). It can also include purposeless and excessive motor activity without obvious cause (catatonic excitement). Other features are repeated stereotyped movements, staring, grimacing, and the echoing of speech. Although catatonia has historically been associated with schizophrenia, catatonic symptoms are nonspecific and may occur in other mental disorders"

Some general information on How to Spot and Treat Catatonia (PDF) that does mention Autism.

Here are powerpoint slides and here is a link to Dr. Ruth Aspy presenting Catatonia and ASD: Hidden in Plain Sight, Part one video. Here is a link to part two slides where Dr. Barry Grossman speaks to the waxing and waning nature of the condition, Part Two video.

Dr. Shah is at the forefront of identifying catatonia-like individuals and wrote a book to describe cases and her approach, which involves assessing an individual's life for triggers that induce slowed responses and reducing as much stress as possible. Here is a link to her book and below is a youtube video of 4 minutes run time of Dr. Shah explaining.