Risperdal/Respiridone is a very strong antipsychotic that is usually used in Schizophrenia, BiPolar etc

From what I understand, if it is being used "off-label" to treat your son ie he doesn't have those conditions that it is normally prescribed for, then it can cause all sorts of side effects that may be considered "rare" -

I did notice "sleep disturbances" and possible hallucinations/ increased psychosis on some of the side effects listed on a Google search.

Here is one link that has a long list of them - Common and Rare Risperdal Side Effects

Just an example to give on how sometimes even over the counter meds can cause intense side effects - some people get sleep paralysis and strange hallucinatory effects that are like dreams but they are awake and in that "paralysis" mode from Tagamet (an acid reflux OTC med) - this happened to a family member of mine, and I have since found even more reports of that effect. That med is now off the market.