What did this for me was Panic Disorder-- not the mild anxiety attacks people get after 6 cups of coffee, but real panic attacks that throw bizarre and terrifying symptoms that cause a singular sense of impending doom. Attacks don't last long but they can mimic (in no particular order) stroke, MS onset, heart attack, bad trip/drug flashback, vertigo, and cancer symptoms. (Note: if you have any anxiety disorder, don't watch House.) It's like your body and brain start trolling the shit out of your mind. Developing it was horrible and cost me my job and my girlfriend-- but I had a really great job and girlfriend a year or so later. On the whole, my life is better than when it started.
I don't mean to trivialize PD. Some people crumble when they develop it and become shut-ins. All mental illnesses are terrifying and awful. I was lucky enough to have the resources (access to some good doctors, great yoga teachers, and effective treatments-- a mix of self-directed meditation, cognitive-behavioral therapy, and medication) to make the problem 1-5% as severe as what it was when I started. And now I'm actually glad to have had the experience because (a) it led me to make some very positive lifestyle changes, such as my conversion to Buddhism, and (b) it has made me less anxious/fearful overall. The fear that people get when dealing with difficult people? That's nothing. No, seriously. It's nothing. If I can go from sheer terror to calmness in four minutes and be fine, I can deal with difficult social situations, as they say on Reddit, "like a boss". Panic disorder makes it pretty much impossible for someone to terrify me to even 1/1000 of the worst extent I've experienced.
That said, I wouldn't advise PD if it were elective. Panic attacks are harmless but hellish, and having intense negative experiences is generally considered harmful. Also, the first year is the worst and will generally be spent on drugs that can take the edge off one's creativity. Still, I came out of it a better person. I got extraordinarily lucky in terms of the people and resources I had around me, as well as the relative maturity I had due to the late age (24) of its onset.