Why does my Playbook display unexplainably darken?

I've owned my PB for a couple of years. In the last few days, I've seen the screen suddenly darken considerably. This isn't the brightness control, it's independent from that. If I put it in standby mode and back out, the brightness returns to normal, but soon goes dark again. Sometimes the screen goes almost completely dark - just some fine vertical lines. This happens whether or not an application is running. Sometimes even when the machine is on standby.
Has this happened to anyone else?

Sounds like it's dying, sorry to say, time to go shopping

Blackberry Passport running 10.3.1.1016

It looks like a hardware problem, in which case you're right it's probably dying. Just in case though, I'd like to try reinstalling the OS. Is this possible? If so, how?