He got migraines, then later went blind and bedridden.
(Disclaimer: I’m not a doctor, nor do I play one on TV, nor have I been diagnosed with the item under discussion).
A quick search shows headaches as consistent with secondary syphilis, but headaches are consistent with all kinds of things. Blindness is sometimes seen (sorry) in tertiary syphilis.
Before Larsen becomes bedridden, does anyone remark that the Cap’n walks strangely, say, with a “stamping gait”?
Pinging some whose general or medical knowledge might be helpful.