Why did my iphone 4 screen turn on by itself?

So my iphone screen just came on by itself, and has done it a few times. No notifications or anything just the lock screen lit up like a ghost… Why would this be? It's driving me crazy! I have the latest ios7 update, it is really freaking me out because it just turns on all by itself.

Legend says: once you update an iphone 4 to ios 7 a ghost will come and haunt your phone. Then it'll come to life and hump your ear whenever you pick up your iphone. The end

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