Like Owner, Like Laptop

So I came home after about, oh, 13 hours, and found that my closed shut Dell Inspiron laptop had been awake this whole time. Needless to say it was a bit warm though it's cooling off now. I'm amazed it didn't shut itself down or crash. I suppose perhaps it's been spending too much time with me, but it's a bit worrisome to me that it wasn't "sleeping" when it should have been. If you have any ideas why, please let me know.