There was a special on the History Channel recently called "The Real King Herod".
The show offered a new (at least to me) diagnosis of the illness Herod died from. The physician they consulted said Herod had untreated kidney disease and also gangrene of the scrotum. Once the flesh of the scrotum falls off it evidently reveals a "worm-like" structure around the testicles. There was also mention of rotting flesh elsewhere on his body.
Herod may have been in considerable pain, but I personally don't see any signs that he was losing his mind. His final will was very lucid and carefully constructed to replicate the political situation at the death of King Solomon. Herod had worked very hard to pattern himself after Solomon and this seems to have extended even to what was known about Solomon's physical deterioration at the end of his life. Therefore, we have to suspect that at least some of these ailments of Herod were not real but faked in order better play his chosen role.
If you recall, Amenhotep III (the "real Solomon") died relatively young (early to mid-fifties) of severe skin problems and other complications from having "denied himself no pleasure". If the mummy labelled as Amenhotep III is in fact his own, it indicates that the skin of his face was almost completely eaten away prior to his death.
© Charles N. Pope, US Library of Congress. All rights reserved.