I'm glad the DVLA were notified.
Here's a scenario of some of the potential consequences:
Diagro is out driving a short journey, he doesn't feel any tiredness symptoms. Another driver rear-ends him at speed whilst he's changing lanes, crushing his vehicle against a concrete bollard, this crushes his legs and pelvis leaving him for a very long stay in hospital with questions about whether he'll walk again. Clearly, this is horrific, but it happens. The fact is that in this scenario Diagro has done nothing wrong in his standard of driving and it's 100% the other driver's fault.
As part of the investigation around causing serious injury through careless/dangerous driving, the police discover the unreported medical condition by requesting his medical records. Diagro hasn't disclosed anything about his diagnosis as he didn't think it was relevant. Questions are then asked around Diagro's driving and whether he was conscious during the crash (Diagro has no memory of the crash due to the trauma) and whether his driving contributed to the collision. The CPS ultimately decline to charge due to unrealistic prospects of conviction. The police consider prosecuting Diagro for the non-reporting of medical issue, but they also drop this as it's not in the public interest considering the injuries. The other driver has no further action against them, despite Diagro's life-changing injuries. Diagro pursues a personal injury claim as he can no longer work and needs constant care. Due to his unreported medical condition, his compensation payout is reduced by 40% and his legal fees swallow up a large proportion of the rest. The compensation doesn't cover all of his costs and he has the added stress of financial issues during his long recovery.
These are the real-world consequences of decisions such as these.
Edit: it's also worth noting there are two separate offences in regards to failure to notify of a medical condition. It's an offence to just not to notify of a new or worsening condition which is a fine, if you're caught driving as well, it's a fine and 3-6 points on conviction.