I’ve just watched it too, but could not relate strongly to his symptoms, as I’ve never had ON, and didn’t have a noticeable issue with clumsiness or dropping things (I would say there’s been more of the latter over the years, but not in the early days).
Having said that, I realise that due to the extremely variable nature of the disease, they wouldn’t be able to pick symptoms everybody has, and those symptoms I did have, such as numbness, would be very difficult to show on film, unless you rather artificially inserted it into the dialogue, so the character told you what he or she was feeling.
On the whole, I thought they did it well, even though I never found myself saying: “Yes, it was just like that!”. Overall, I thought they went for “less is more”, so didn’t dwell overmuch on exact symptoms or diagnostic procedures (although we know he had an LP). I think the more detail they try to cram in, the more chance it won’t ring true to anyone in-the-know, so they left it at enough to understand what’s going on, without overdoing it.
Now they’ve started, though, they have to carry it on for another three episodes, so it will be interesting to see whether they show him as being largely OK, and choosing to keep quiet about it, or facing increasing difficulties, to the point he can’t keep quiet any more - and perhaps can’t keep his job.
It paves the way for a dramatic dilemma about whether he has to quit in the final episode, but if they give him RRMS, they can still leave it open for another series, as they can say he made a brilliant recovery! Crafty dramatic choice, to give the main character MS, as you can have it turn out however you like.