Nexus 7 randomly goes into sleep mode

[Hackmuss]

Hi there. I recently got my Nexus 7 (thank you Santa  and although I am generally very happy with it, I do seem to have a small problem that I hope you guys and gals can help me with.
Occasionally (it's done it about 5 times so far...), I am using the tablet (usually in a game - the last time while playing Angry birds), and it suddenly goes into sleep mode for no apparent reason.
When I hit the power button again, I get the lock screen up - but as soon as I swipe to unlock, it puts itself to sleep again. It will do this numerous times. The only way out is to get to the lock screen and then power off the device completely, then power it back up again.
Any idea what might be causing this issue please?

[fxsarge]

I bet its one of the other apps you have installed. If your comfortable with listing all of your installed apps we can help identify any culprits. If we don't find anything unusual I would recommend a factory reset as a last ditch effort followed by a warranty claim if that doesn't help.

[loociddreemr]

Do you keep your Nexus in a case? Some cases have been known to cause this.

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