sometimes the tooth can become sensitive due to the agitation of drilling. this will calm down in awhile. if it doesnt get better or if the pain increases you could need a root canal. relax and take an over the counter pain reliever it probably will go away. sometimes it takes weeks. i dont know why the dentist would only give a day before deciding to do a root canal except for situations of extreme pain.
you may not need one now you will be cover for several years if you keep a good diet but fillings don't last forever so now that you have a big filling in your teeth you need to make sure you see your dentist every 6 months along with a health diet ..no more waitng 2 years ... i had a big filling once now its a crown with a root canal GRRR
If a cold stimulus provokes tooth pain lasting longer than 10 seconds, it suggests irreversible pulpitis, in which condition, root canal treatment is indicated. Your current presentation doesn't suggest irrecersible pulpitis. You can wait for a couple of days.