Possibly relevant: Festival of Dangerous Ideas: Panel - The Price Of Modern Life Is Depression And Loneliness.

One of the main points I got from that is that it is not at all clear that mental illness is growing, because one thing that has definitely been growing is the sensitivity of diagnosis and if there was any growth of mental illness it'd just be obscured by that.

I'd add that alcoholism can mask a lot of smaller but more complicated mental issues, and since alcoholism is going down, those should be becoming more visible.