Why is part of my bottom lip numb after I got hit in the mouth?

I got hit in the mouth about 3 days ago and since then, I cant feel the left side of my bottom lip. My lip is not busted but there is a small cut on the inside further down on that side (facing my gums instead of on any visible part of my lip). I have had a busted lip before, and even cuts similar to this but I do not recall ever not being able to feel my lip. I mean, I can feel the wetness if I lick my lips and it kind of tingles (like when your foot is asleep) when I touch it, but for the most part it is numb. Can you explain why the left side of my bottom lip is numb?