I don't think Miles was spiked. I'm not discounting the possibility, but it seems a difficult enough art that he couldn't be spiked accidentally, and nobody was in the position to spike him on purpose. About metalminds, remember that they don't have to pierce the skin. That being said, I wouldn't be surprised if Miles did pierce his skin with his, seeing as he's often dealing with Lurchers and Coinshots when tracking down criminals.
I'm more inclined to believe that any insanity in Miles derives from being shot in the head too many times. I don't care how perfectly/rapidly you can heal, a bullet through the brain is going to have mental repercussions. They would be slight, but enough bullets through the brain, and you'll be left with at least some instability. Remember, also, that Miles had difficulty healing his eye when some fabric got trapped in there when Wax shot it.