Tooth decay

Hi, I have a cavity issue with my molar. In the beginning, I thought it will get reversed on its own so that I controlled my sugar and sticky food consumptions!
Unexpectedly, now it has become abstruse. I don’t know why maybe it is because of my habit, that I used to clean inside the cavity while brushing and after every meal(mostly I used toothpick and pins)! Due to discomforts while eating and slight pain, I consulted a doc in Toronto, I had a detailed scan. Literally, I’m kind of depressed by knowing that I need an emergency root canal pain treatment, as the cavity has become deeper so that filling won’t be useful anymore! I regret my actions, I could have visited him far before so that I could have filled my tooth.
I’ve got an appointment for tomorrow eve, so I’d like to know what to expect after the treatment. Especially what it feel after the procedure?