Wait, so is your son being given Invega (presumably the once-a-month version, right?) AND risperidal at the same time?
Because that sounds like it is indeed too much.
Technically, the second shot of Invega is supposed to be less strong than the first. 4 days is also the bare minimum between the first two shots.
What's more, the idea behind the Invega shot is to eliminate the need the need for taking risperdal pills on a daily basis, at least temporarily. If the patient has been stabilized on the shot for the time being, they can then switch to the pills, but I question the wisdom of giving someone two shots (one of which is overdosed) AND immediately starting with the risperdal at the same time.
The problem with these drugs is that some doctors see these as chemical straightjackets, which I guess to some extent they are. However, in an acutely psychotic patient, they are unfortunately sometimes necessary. Depot shots help ensure compliance when the patient is not yet stable enough that they can be expected to reliably take their pills on a daily basis. However, in the long-term, it would be preferrable if the patient comes to the realization that the shot was an unfortunate necessity for their safety and that of others, and that it would be in their own best interest to try and work with the docs to find the optimal treatment. Going with a "better safe than sorry"-attitude and administering a highly unpleasant overdose will often just result in the exact opposite consequence, i.e. a patient who's even more paranoid, and less likely to comply with their treatment regimens.
On the upside, it is very unlikely that your son has actually suffered physiological damage. This condition of restlessness is called akathisia, and it will indeed disappear over time, and/or it can be mitigated once the right combination of meds is found. If he's not shaking, that atleast suggests the drug isn't blocking an extreme number of dopaminergic receptors (although I would suggest speaking to your doctor before giving him benadryl/diphenhydramine, because it could mask certain side-effects, and even intensify cardiac arrythmias).