A catatonic state can be caused by schizophrenia (which is what I always pegged Henry as as soon as I found this stuff out b/c that's what they think Grandpa had & that can be genetic), or even severe bipolar syndrome, autism, or PTSD (maybe Jack Cade really scared him :-O).
But it can also be called by that whole tse-tse fly sleeping sickness thing (which we can rule out as Henry didn't go on safari to Africa like Harry & William) that's a form of encephalitis, a drug overdose (medieval medicine....'nuff said), or in the aftermath of a stroke.
So since Henry was about 33 at initial onset of this recurring state, maybe he wasn't mentally ill. Kind of late in life for really severe bipolar to make itself known & Henry was never observed to be manic, just naive & not the sharpest quill in the royal writing box. Autism also would've shown up a whole lot sooner. He could've developed PTSD from watching Joan of Arc toast when he was taken over to France to be crowned as a child....he supposedly did fret, w/ how devout he was even as a kid, that she really was a saint....but I can't think of anything else in his sheltered little life up until that time, except for Jack Cade's Rebellion, that would've been traumatizing. Not to say that there couldn't have been some abuse in secret, what w/ him being in a separate household from his mother & surrounded by power-grubbing uncles & other men since he was still in diapers.
Maybe Henry got too much of some "strengthening tonic" w/ oddball ingredients no one would ever ingest nowadays....medieval medicine was more likely to kill ya than cure ya. They sprinkled wounds w/ powdered pearls, for Pete's sake, regularly took a pint of blood out just b/c they could, & spent an inordinate amt of time sniffing royal urine & stool samples to see if the king's "humours" were in order. Who knows what sort of stuff Henry was being fed, & he'd be the type to knock it back unquestioningly if told it was good for him.
Or maybe he just had a series of strokes. The catatonic episodes weren't frequent & there weren't a lot of them. Never realized strokes could cause that b4. Mr Google is my friend LOL
Still can't rule out schizophrenia w/ the hereditary evidence, but there are times when doctors think ppl are just mental when they have a physical ailment even today (fibromyalgia leaps to mind). If Henry was nuttier than a fruitcake, the current crop of royals are lucky that schizophrenia left the gene pool, w/ his poor begats showing :P
In looking at the "markers" for schizophrenia, psychologists have 2 sets of them, positive & negative.
Positive ones are the more obvs ones that are likely to raise an early alarm for mental illness, like hallucinations (incl those involving the 5 senses), hearing voices, paranoia, delusional behavior, your basic psychosis brewing. Sitting in a corner babbling about monsters coming after him would make ppl think Henry was insane, to give a simplified example. Him thinking his meat tasted green or smelled like red roses or felt like velvet on his tongue wouldn't be noticed. Paranoia to a degree was expected *healthy* behavior in a king, esp w/ a powerful cousin like York in the opposition camp.
If Henry wasn't having the screaming meemies type of hallucinations & kept his little *oddities* to himself, who'd see it?
Negative markers are more subtle, like lack of motivation, lack of emotion, sparse &/or monosyllabic speech, wanting to be alone, inability to enjoy life, things that wouldn't shriek "Hey! The king is nuts!" at the ppl surrounding him.
There's also the aspect of Henry's extreme piety, the main reason he was able to hang onto his throne as long as he did. He was revered as saintly in addition to that whole divine right of kings thing. So if he went & knelt at his prie-dieu for hrs & didn't want to be bothered, his household would just think the king was deeply involved in prayer, as God's appointed monarch ought. It wouldn't occur to them that he was in a light trance, listening intently to the voices in his head, deliberately avoiding socializing or responsibility, etc. God & prayer was a huge part of life & it was important.
So that's why I don't think it can be entirely ruled out. He could well have been having symptoms of schizophrenia that went unremarked, mainly b/c ppl already felt he wasn't quite *right* to begin w/. Most ppl are diagnosed by age 20 or so. No medieval shrinks, tho, to do so. As long as Henry wasn't acting out violently or weirding out in public all the time, meh. He was thought to be a bit slow & stupid anyway (maybe he was mildly brain damaged from birth) & was constantly wandering off to go pray & meditate, leaving the kingly work to his councilors. They got goodies for that; are they going to object?
But yeah, because this episode of crystal-clear WTF didn't arrive until his 30s, he could just as well have suffered from strokes. You'd think it might've been earlier in life if it was schizophrenia.