Sorry to hear about your diagnosis.
I’m not a driver, but I’ve been around on this forum long enough to know you have to inform them, by law - it’s not optional, I’m afraid.
Also, you should inform your insurer. For some reason, when this subject has cropped up in the past, it has sparked huge controversy, with some claiming the insurer does not need - indeed has no right - to know.
However, they are not allowed to revoke your policy nor hike your premiums purely on the basis of your diagnosis, so you have nothing to lose by telling them, and will ensure you are absolutely squeaky-clean in your dealings with them, as most if not all insurance policies are based on you having disclosed ALL material facts - including health issues - whether or not this would affect the premiums.
It seems some insurers are in the habit of replying: “We don’t care, what are you telling us for?”. BUT, if you tell them and they’re not interested, that’s up to them. Conversely, if you don’t tell them, but they are interested, and try to use it to void the insurance if you have an accident, the problem will be yours. So my view is that as there can be no adverse consequences if you tell them, but plenty if you don’t, but they think you should, you cannot be in the wrong by telling. For the price of a stamp or phone call, you will have peace of mind, knowing your insurer cannot, following an accident, turn round and say: “But we had no idea you were ill! That voids your cover!”