It is possible that Windows Update encountered a glitch and you ended up with a corrupt video driver installation.  First step with video problems should always be to go download the latest certified drivers from the manufacturer and run the install manually, bypassing Windows Update.  If the downloaded drivers are newer than the ones you have installed right now, then you will replace the drivers altogether.  If the drivers are the same version, then you will still get an option to repair the installation.

The fact that you need to boot into safe mode to recover is also an indication that it is a driver issue, since safe uses generic drivers for most of the hardware.

I suggest you give this a try and see if that solves it.

Thanks for the advice.

Using the Properties 'tool' associated with the video driver I 're-installed' (I was up-to-date) - and so far so good.

But of course I can't be sure that's fixed the problem! I guess I just have to wait and see.