Something to consider about PAW mental illness is a lot of the folks now considered mentally ill will actually be more functional in the chaos of PAW and the people who are not mentally ill now will have a much higher likelihood of becoming mentally ill.
What I mean is a lot of the so called mental illnesses of our current society are adaptations for a different set of society rules. For example ADD and ADHD are not really mental illnesses as much as they are actually human adaptations to hunting. ADD and ADHD people are hard wired as hunters, which tends to cause problems in an agriculture based society. If your interested in this concept there is a lot of information on line about it. Here is one example http://borntoexplore.org/hunter.htm
to get people who are interested started.
Further a lot of the people who are depressed are depressed due to feeling trapped in a pointless or otherwise meaningless life. I have often heard from depressed people how they dislike feeling like a cog in a vast machine and that is what depresses them.
In PAW a lot of the causes of these current metal illnesses will be gone. Not all, but ones like those I mentioned above that have their roots in not fitting in with current society. If the folks with these issues survive they will likely become much healthier mentally. However the folks who were considered just fine, will be suddenly out of their element. Remember how I mentioned ADD and ADHD is an adaptation to hunting, well obviously the "normal" people are the adaptation to agriculture. If suddenly they loose that way of life (and especially have no knowledge about how to rebuild agriculture based society) they will be just as disoriented as the ADD and ADHD folks were in the agriculture society. While the currently depressed people might wake up from their depressions when suddenly facing serious life and death situations and a more active role in day to day existence, the folks who were fine with their normal lives will be devastated by the sudden lack of it and likely will spiral into depressions.
Also along with the concept of mentally ill wandering around unmedicated and unchecked.
I lived in Philly. The largest mental institution in the US, Byberry http://en.wikipedia.org/wiki/Philadelphia_State_Hospital_at_Byberry
, was in the suburbs of Philly but got shut down in the 80's. The result, they literally kicked thousands of patients into the streets. Of course they would hand them a piece of paper saying go to this place to meet this doctor to get your meds. Guess how successful that was, LOL. So Decades later there are still crazy homeless wandering the streets of Philly. Literally screaming at lamp post and trash cans like they were alive but not even seeing the people as alive kind of crazy. After awhile you get pretty good at spotting the mentally disturbed quickly. One interesting thing that I have found that seems to get through to them. Crazy people avoid crazier people. If you end up with trouble with someone mentally disturbed bothering you, the most sure way to get rid of them, is to act crazier than they are. Start drooling and talking to invisible animals, jump around and flap your arms, make a complete idiot of yourself and 90% of the time the other guy will get scared of you and take off. Odd and weird but it really does work. What about that other 10%? Well that is the scary ones, the ones who start matching your crazy with even crazier. If that starts happening run, seriously get out of there. Those are the most unpredictable mentally disturbed people and you really never know what they might do.