Never seen this before, thought I was screwd

[Saint Michael]

So I put my Lumia 920 down on the charging plate, then noticed that the volume was showing, and it was at 00. So I tried to turn it up - it wouldn't. So I shut it of, when putting it back on, the display turned black after Nokia and then a big explanation mark. What does that mean? Works now, several reboots later, but that freaked me out

 

[Joshoon]

Isn't that what appears when you want to hard reset the device? I have read that somewhere that if you want to hard reset it that you have to use other hardware buttons on the side when the explanation mark appears.
As long as you did not pushed any of those, and the device is booted right now, you should not worry about anything I guess