Screen fades to black and back again

[spasell]

I'm not sure if anyone else has had this issue, but recently, a few times, I'll be just typing on my x61T and all of the sudden, gradually, my screen will fade to dark, much darker than just reducing the backlighting. It's almost 100% black, except I can just make out the background. All of the sudden, the screen slowly starts to regain the backlight, until it goes back to bright.

Does anyone know what this might be? I am running Windows XP. When this happens, I am either on my Outlook checking emails or I have been printing up pages for work. Another time, I was simply on the internet and it started that process. The entire thing lasted about a minute or slightly less. Very strange.