I actually have no idea how "normal" people feel and whether I have numbness or not. But I don't think I am in danger of muscle damage, with fast practice I don't mean anything extraordinary, just repeated action to gradually soften my limbs 
I'm totally stabbing in the dark here, but a bit of reading suggests that you may be less likely to sustain performance injury than the rest of us because you may be unable to over exert yourself in the same way.. depending on the severity of the condition...
Sounds as though fast and vigorous warm up would have to precede your slow work. So that the muscles are properly 'loosened' and you can actually practice the proper release of the muscles during slow practice..
..and that the following day/session you would have to limber up again before the same muscle memory patterns could be activated.
Edit:
It reads as if while most of us experience tension as a result of overexertion, you are far more likely to have limited activation of your fingers caused by a mental block as such, so over exertion is unlikely... unless you really force something, which may explain your experience with the 5th finger.. in that keeping it down resulted in a problem. I suppose you kept it down by activating it and fixing it there rather than taking away the unnecessary lift.
Not sure if that means its harder for you to fix that issue or not, could still just be a differnt thought process required. Hmmm.