Barry Schwartz posted an interesting article not long ago about a Webmaster World poster that claimed he considered killing himself after Google devalued his site in the SERPs. As a result the poster's business was killed, as SEO was it's only marketing channel. Now of course any business owner than is hit that hard over night is going to go through some serious mental and emotional distress, but to me it seems that SEO is the perfect storm for fostering and attracting emotional imbalances.
Think about it this way, in a very real sense, SEOs have an immediate measurement (in the form of SERPs and traffic) of the success or failure of their work. The coveted #1 position can be the peak of a SEO's career, and the sudden fall from #1 to even #10 can put a business on it's knees. Those that thrive off of instability are maybe attracted to this line of work. And those that are prone to emotional instability might be ruined by this type of work.
This type of instability can have similar effects on other industries, so it would stand to reason it can happen in SEO. Do we need to spend more time as a community talking and considering the mental health of our colleagues?