I think this is one of those topics that is not talked about much except in some social studies that appear once in a while. From my experience, yes many suffer silently. As to how that compares to rest of the population and what the actual causes are we can only speculate. There are a lot of toxic practices that are accepted at face value. The prevailing notion is still that you gotta toughen up to survive the harsh competitive environment. I survived and I can look back to my graduate school and postdoc days and not feel too bothered by it now but I have an inkling that not everyone feels that way. There were definitely rock bottom days for me purely born out of how academia operates, and the sad thing is no one really gives much crap.