I feel like this isn’t acknowledged in discussion, fanfics, or even fanart involving him as much as I thought it would be, even though it’s something that is, as I see it, an important part of his character.
It’s been established that he walks stiffly and carries around an umbrella despite good weather. Why? Because otherwise he would be walking with a limp, due to whatever childhood incident lead to him being stuck in a bed for years.
Yes he walked without the umbrella at times, but he was still described as walking stiffly. Plus: Dynamic disabilities.
He had poor eyesight. This was both because of whatever childhood accident he had resulting in him not being able to see out of his right eye very well, and general poor eyesight. He has a long scar from on his eyelid to his hairline, which he covers with his hair. I see a lot of ‘emo’ jokes about this, which I’m not saying not to make, they’re funny, but I think there’s also the possibility he did it because his eyes were fucked up and too much light hurt his head, especially if it was too much light through his right eye.
His headaches. He explained himself how awful they are, how debilitating.
He even had to take medication that was so strong he couldn’t just get it prescribed:
While he doesn’t mention it here, we see later on at Bunny’s funeral, when he’s having one of those migraines, that he also gets shaky and sweaty because of them. Yes, some behavior is influenced by the fact he was at the funeral of his best friend which… he killed. And he was spending time with Bunny’s family. Nevertheless.
Plus, there's the little pill box with medication (which I’m going to assume was mostly pain meds, but it could’ve been other stuff), the one he kept on his person, in his breast pocket, because he dealt with this and was prepared.
And those are just physical. He’s also autistic, or neurodivergent in some way (in my opinion). While some people may disagree, or think differently, it’s not an unreasonable conclusion to come to. I mean: He would go on and on about whatever he found interesting at the time (infodumping). When he prepared his own food it would be very plain and simple (safety in predictably). He tended to be blunt. He wore pretty much the same thing every day (stuck to routines). I could go on. That said, I’m not a medical professional and can't actually diagnose him (I’m just peer reviewing him here as a person on the spectrum) (I still think it’s true).
It wasn't just 'ouch headache' sometimes, it was an umbrella as a substitute for a cane, him keeping medication on himself (for the migraines), him trying to minimize issues with his eyesight by shielding his eye.
