This is not the first time Horikoshi has taken time off. He also skipped a week in June due to illness. It has been not specified what type of illness Horikoshi has, nor whether both mini-hiatuses were due to the same cause.
In July, Japanese fans ranked Horikoshi as one of their favorite manga authors.
Manga schedules can be quite punishing, and manga authors have been known to push themselves to the limit, which can eventually lead to more serious health issues (and longer hiatuses). Here’s hoping Horikoshi gets the rest and treatment he needs.