being a big youtube star can be stressful man. im not saying its a 9 to 5 job stressful but they have their fair share of stress. they have to edit videos (which can take a while depending on how heavy they edit), deal with death threats, upload at least once every two weeks to get paid, do whatever is popular so they don't get irrelevant, and if one video goes down due to some fair use copyright bullshyt it could easily mean the end of your channel.
Filthy frank got seizures from stressing himself out with videos. I Hate everything almost had his youtube completely removed for no reason causing lots of stress, etc.
lets also not forget the mob mentality lots of big youtube stars can start. if pewdiepie say's you're a stupid piece of shyt then your youtube channel is over and you will receive countless death threats so you have to be nice to everyone even if you don't like them.