Shocks after Root Canal

[Kate white]

Hello, I went to my dentist to have a root canal treatment done on my back lower molar. He missed a canal/nerve and within 24 hours later I started having extremely painful shocks through that tooth. He now thinks that the filling substance was reacting with the live nerve. I have since been to a specialist who has completed the root canal treatement. The shocks stopped after this. However my gum is still sensitive to brush or to eat, I have been back to the specialist and he has confirmed that the root canal looks perfect and also checked the height to make sure I'm not hitting or grinding it.
My question is how long does it take for the gym to heal and also has anyone ever experienced this before? Many Thanks Kate