I withdrew from taking 2mg Risperidone a day for a bit over 6 months and there was definitely a lot of rebound symptoms, especially insomnia for me. I would expect things like weight gain and low blood pressure upon standing to get a bit better, but your mental health can definitely go down hill. I was getting some hallucinations, worsened insomnia, and in general a really noisy head with lots of "word salad" voices. I tapered over about 2 weeks but in retrospect I would've gone slower, as I wasn't getting back to baseline-ish for about 2 months. Anti-psychotic withdrawal is no joke, 2mg for 6 months is a wimpy dose/length of time too. I would be very cautious about higher dosages and/or being on it for a longer period of time. I think rebound symptoms is a guarantee.
I think what happens is that when we're on a drug we feel better so then we think "Well I feel better so I don't need this drug anymore", when really its the drug that is helping us.
To understand whether a drug is effective or not, we run a trial that is placebo controlled - so while some schizophrenics are receiving a sugar pill, the other schizophrenics are receiving xyz drug. If 6 months later more schizophrenics have remitted while on the active control (the anti-psychotic) compared to the schizophrenics on placebo then that is enough to say that it is effective. Clozapine notwithstanding, I believe we can get about 30% remission with antipsychotics. With clozapine, that number increases to about 50-60% (correct me if I'm wrong Ho-Chi).
But as far as the exact mechanisms of the drugs we are indeed still in the dark. Schizophrenics generally don't respond to anti-psychotics until a few weeks in, hinting that there is more going on than the acute effects of the antipsychotic - dopamine receptor blockade - there are probably genetic mechanisms downstream of dopamine receptor blockade that are truly responsible for the efficacy of antipsychotics. In general, most meds take a few weeks to respond to, so to a large degree most meds are thought to have a genetic component to them, which we haven't quite unraveled.