ASD and schizophrenia share something in common: Both feature NMDA receptors functioning differently than in neurotypicals, which is a plausible cause for why some people are able to tickle themselves.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3808979/

https://pubmed.ncbi.nlm.nih.gov/17097347/

People with either are less likely to experience illusions. SlateStarCodex had a decent article that touched on the phenomenon a few years ago:

https://slatestarcodex.com/2017/06/28/why-are-transgender-pe...