The Oxford Handbook of Nietzsche
Oxford University Press
This article examines how Nietzsche’s illness bears on his philosophical ideas. It demonstrates that the long-standard explanation for Nietzsche’s dementia—syphilis—is almost certainly false. The cause is much more likely to have been a brain tumor, which had caused him severe headaches and eye problems since childhood. Nietzsche also suffered from a host of digestive problems. It is no wonder that he puts such great weight on “health” and especially the kind of health that overcomes sickness and suffering. When Nietzsche values “madness,” it is a healthy and philosophical madness exemplified in Zarathustra and which Nietzsche tried to cultivate in himself.
Huenemann, Charlie, "Nietzsche’s Illness" (2013). Languages, Philosophy, and Communication Studies Faculty Publications. Paper 395.