You may have been sleeping on something sharp, like a piece of plastic.
As to the dream, it's interesting to me that you describe the assailant as a teenage boy. Do you work with youth? If you are in an environment where teenagers roam and they are frequently insulting you, or being rude to you, the knife can represent their attempts at hurting you.
They ruin things, certainly. But they don't get to you.
Similarly, there's the metaphor of betrayal that's common with the concept of "stabbing in the back." Have you been recently betrayed or lied to by somoene you thought you could trust?