Its not always streight forward as replacing your licence with a 3 year one. On a non diabetic related illness I notified DVLA via phone and was sent the appropriate forms, I filled them in, the next thing I heard was I had a letter giving me 3 days notice that my licence was revoked.
They then sent for all my records from the hospital and , to investigate my condition. It took over a year to get my licence back by proving I had been sorted out and was using the correct treatment. I still have to have annual reviews and if I don't pass the review I loose the licence again.
On a diabetic related illness, I again went through the notification process feeling the worst would happen again. I recieved a letter saying to return my licence as it was going to be replaced by a 12 monthly renewable one

. as part of this review they revoked my entitalment to drive certain catorgories of vehicle.
DVLA sent a remider 9 months later asking me to reapply for my licence, which I did. DVLA then wrote to the hospital and doctors again to see what my condition was, this took a lot longer than the 3 months I had left on my licence and I had to get a letter off them to say I could continue to drive while investigations were on going.
After a good while I had my licence back as a ten year replaceable one, still without the entitlement to drive certain catorgories of vehicle and the licence was endorsed on the plastic part with extra codes. So if I was stopped and I was not complying with the codes I could loose it again.
The anoying factor is for me, is evry year since I go for the checks ups and there is no sign of the condition that caused the restrictions to be put in place. Due to reporting them and as at the time I was supposed to have had the condition, I can't get the catorgories added back on to my licence and the codes lifted.