IIRC Togashi said his work started giving him nightmares and shit, I think the dude went too deep down the rabbit hole doing research for chapter black 😂
But yea I don't really buy the health issues. It's part of the lifestyle of a mangaka, Togashi just uses it as an excuse to not write/draw. Which is fine tbh, if you were one of the best in the world at your craft, made millions, and were still forced to work slave hours, most people would look for a way out. Togashi found what works best for him, draw a volume every couple years and blame his health, one time he conveniently came back when Japanese bookstores said they were removing HxH from their shelves. I shit you not a few days later he made an announcement for his return.