I was part of a Zen meditation group for about six years. I did not personally notice members having psychotic breaks during retreats. What I did notice was tha

I was part of a Zen meditation group for about six years. I did not personally notice members having psychotic breaks during retreats. What I did notice was that people were coming in with depression and anxiety, and that the mindfulness practice was not helping to drive people to manage the issue. They were just comforted by being in the presence of other people who had similar issues they could relate to. What I found upsetting was that the leaders of the group were not interested in actually solving these issues either and were perpetuating the state of being present with the problems the meditators had. This created a vicious cycle of dependency. Anxiety and depression are not things you can just figure out and snap out of. As a commenter mentioned earlier, the point of meditation (in the Buddhist context) was to facilitate ego death. Watching the self, knowing the self, and extricating the self, in order to be freed from the problems of self (which is thought to be causing the depression and anxiety). In our modern context most of us can't go into a forest refuge and isolate ourselves to do this practice.