Stress
Like all entrepreneurs, YouTube video makers deal with the harsh mistress that is fluctuating paychecks. Oh hey, you made $15,000 this month. Good on you. Oh hey, next month you only make $800. Well, we hope you didn't spend that whole big check in one place.
Fame can also be responsible for a large number of stresses, not the least of which is the judgment of others. Once you share yourself with people publicly, they sort of get the notion that they have a "right" to a piece of your life, and typically won't hold back when they're not happy.
Make a bad video? Hold a controversial opinion? Leave a less-than-glowing tip at a restaurant? It's all controversy and comment fodder, and you'd better get used to it because there's no getting away from the harsher side of the spotlight.