Crack in windshield

So last night on my drive to work, I noticed a crack on the drivers side windshield, I can't see where anything hit it to cause the crack, and there isn't any spider webbing, it goes from the very edge of the glass to about halfway over the first defrost vent, at about 3 inches below eye level. It's very noticeable, and I definitely would have noticed if it had happened when I was driving, and it happened on the side of my car parked away from the road. Im not sure what I'm going to do, and I wish I knew what happened. I'll ad pictures later, I have to go to sleep, and forgot.