Oh yes! I also fear being numb. In fact, I'm numb right now after coming from the dentist (crown prep) and trying not to freak out too much. Here's my experience from today: some of the numbing medication did go to the back of my tongue while the needle was withdrawn, but I had a dental assistant suction it really good and that helped. And that numbness didn't last long at all. Half of my tongue is numb, but remember that the injection doesn't numb the back of the tongue, so you will be able to swallow just fine. And the medication does not impair your muscles at all. It just feels weird!
Others on this forum have told me that there is a "reversing" medication they can give you after your procedure to reverse the numbness. Call your dentist before any procedure and specifically ask for this to be available.
So, yes, dental numbness is a very real fear and many of us have it. I tell myself that the numbness is better than pain and that everything in my mouth still functions while numb. It really is "mind over matter." I'm getting a little better at it, but being numb will always be one of my fears.
Hang in there!
Laura