Of course I can't claim that my personal experience is representative of all people. But you're the first person I hear say that did not feel any psychological effects of doing a PhD.
Every single person I know that did a PhD (including myself) has mentioned feeling frustrated/isolated/depressed/etc at different stages in their PhDs. It is interesting to see that some people are actually not affected that much.
I guess I'll just chime in and say that, going into my fourth year, I've never felt frustrated/isolated/depressed more than I thought was normal. (I mean, does getting frustrated with GHC count? :P)
I'd actually say it's the opposite: the process of getting my PhD has been one of the more wonderful experiences of my life thus far. Although, I tend to believe that at least part of this is due in large part to one particularly awesome professor that I've worked closely with (and isn't my advisor).
Every single person I know that did a PhD (including myself) has mentioned feeling frustrated/isolated/depressed/etc at different stages in their PhDs. It is interesting to see that some people are actually not affected that much.