1st I searched and I like the new popup feature telling us of similar threads

Yesterday as I was typing (during a class and holding w/my left hand and probably covering the light sensor) the screen started fading, from left to right, like sunset was going on.
Eventually,over the course of about 5 to 10 seconds, it went totally dark and the 810 shut down.
Can we say panic?
After several tries i was able to turn it back on, it still had over 50% battery (per battery status).
It's been running fine since, and saved my latest few words in Maemopad+.
Have others experienced this?
The keyboard was out.