Please note the above name - Dr_BS_MD. I doubt very much if this person is a medical doctor (also note the medical spelling error).
First, psychologists are not physicians and cannot prescribe medication. Psychiatrists are and can..
Second, the medications given, Zoloft, is an antidepressant drug. The Risperdal is an antipsicotic drug. Both drugs are NOT recommended as a suitable treatment for bipolar disorders. Lithium carbonate it the ideal treatment!
The brain in prepubescent children is wired differently than adults, thus these medication, instead of helping, can actually worsen the prognosis.
Until things clear maybe you should be seeing the psychologist more for support during this time. Also, is your son seeing a child psychiatrist? This has to be a difficult time for you and your family.
Zoloft, as almost any drug, can have bad consequences. The 12 year old you referred to was probably an extreme case (since it was added to his other medications). But it is certainly a good idea to Google it and read all about it.
In my opinion a good psychologist would be seeing your son at least once a month, and would be doing more then just giving meds. Wait. I don't think (could be wrong here) that a psychologist can prescribe meds. Where is the prescription coming from? Which leads to my next point. Yes, I would look for a pediatric psychiatrist.
I can't really answer your questions but I'll state what I do know. I belong to a support group for teachers and parents of children suffering from anxiety. Zoloft is one of the SSRI medications used for the treatment of anxiety. A few of the children in our group have used this medication and did well on it. The Risperdal is an anti-psychotic drug and is not used in anxiety issues (so I assume this is for the Bi-polar aspect of this illness) and so I am not overly familar with that medication.
As for your second question - the symptoms you mentioned could have been the result of very severe anxiety but the "violent" part is upsetting and not common to anxiety issues. Nonetheless, if you are questioning your psychologist, then I would consider seeking another opinion - perhaps from a child neurologist or child psychiatrist. Have you posted this question on the Expert Forum - perhaps the Anxiety or Mental Health forums? Hopefully someone else will be able to offer more information ....