Stress
This might seem counterintuitive, since your entire job is about getting other people to de-stress, but being a yoga instructor can definitely induce anxiety from time to time.
Even though you're not designing nuclear missiles or crawling through the trenches or working under the yoke of some overbearing middle manager, you've still got clients to please and promotions to do—and you likely have to do them when not doing some other job that actually pays your rent.
It can be even worse for the independent yogi. Your days will be chaotic as you rush from studio to studio, and since you're not allowed to pick your clientele, sometimes you have to deal with people who just really don't get yoga. You can pick them out because they're talking loudly on the headset while in downward-facing dog.