If you have doubts then, of course, don’t drive.
But if you feel fine to drive, and want to confirm your are indeed fine to drive, it’s a good idea to put it to the test by trying it out. After recovering from any serious medical problem, it would take a lot more than a spin around the block to convince me I was fit to drive from Durham to London.
And stress again, the 20 metre number plate test does not prove you are fit to drive. Failing it proves you are not fit, but passing it merely suggests you might be fit. Try it, it can be passed with vision that many people would regard as totally unacceptable for driving.
It’s been suggested he stopped during the test drive and went walking. I’d have done the same thing and again, an assistant can help for comparisons’ sakes. E.g. Who can count most clearly the lines on that electricity pylon on that hilltop? Does that gate at the far end of the field have a padlock?