Not being a doctor, this answer will be from a layman's viewpoint, based on online reading of health articles.
First, numbness in any extremity could be the symptoms of a very serious condition, so I strongly suggest that if you have numbness in your fingers, that you have it checked out by a doctor AS SOON AS POSSIBLE!
Some of the possible causes I've read about are:
1. A blood clot blocking an artery, or
2. A mini-stroke in the brain which, I think, is technically refered to as an Intermittant Ischemic Event.
Again, IF you actually have this symptom, see a doctor ASAP!!!!!j3h.