Screen blanks out/shuts down randomly

I have a 16gb wifi ipad, that I just received a couple weeks ago. I use it mainly for web surfing, pdf reading, and ebook reading. I keep it in the apple portfolio case (the one that has the front flap and can act as an incline).

The past couple of days, the screen has randomly blanked out/shut off. At first I thought I just accidentally set the ipad to auto-lock at 2min instead of 5min, but that was not the case. When I press the home button after the screen shuts off, instead of showing the slide to unlock, it just shuts off whatever app I was using and goes back to the desktop. It has happened while using a number of apps, both native and added.

I didn't see anything exactly like this on the board. Is anyone else having this issue and is there a fix? Thanks!