Actually that high a dose can cause motor side effects such as akathesia that can cause agitation that can be mistaken for psychosis. Its important to notice if he has problems pacing or has motor restlessness. Also a dose that high can put someone at higher risk for tardive dyskanesia which I have that is permanent. I would reccomend speaking to his psychiatrist and if the dose is that high for a reason (say extreme psychosis) perhaps have it transferred to something else.
The typical dose is 2-8 mg per day, but that is arrived at gradually. Yes this is a very powerful medication, and does have side effects to worry about. I suggest you educate yourself by searching for information on the web, then talk to your doctor about your concerns.
Actually that's considered an overdose, and yes as the dose increases chances for something to go awry increase. I wouldn't say that's a toxic amount of Risperidal but it would probably put you at risk for a seizure to say the least. If you've taken that much you need to check your vitals.