This must be disturbing. However you need to relax. RCT fills generally don't pop out. In last 20 years, I have come across only one case where the patient told me that she had got RCT filling done at some doc and then at home she felt something come out, some thread like substance which she pushed back in. This is a very rare occurrence. Very rare. In your case, unless you felt some thread like substance popping out, only the temporary filling on top must have come out or a part of the temporary filling has come out. Don't worry. Just visit your dentist tomorrow and get it fixed. Sleep well.

Root canal filling would not have come out. It might be the temporary filling kept on top