Throbbing tooth?

A few months ago I had a cavity filled and the dentist told me that it was deep and make sure that I don't put anything hot or cold for the next few weeks.

I made sure not to eat on that side, or get anything hot or cold on it.

However, this morning I woke up and the tooth was throbbing but after a minute or so the throbbing went away and don't come back.

Should I be concerned?

My dentist said that if the tooth is continuously stimulated the nerve will die and I will need a root canal (in sort of a worst case scenario).