The filling from my root canal came out while i was eating. could this be serious?

Maybe: Once a root canal is completed a temporary filling is placed until the tooth can be restored. Depending on when the root canal was completed it is generally best to get into your dentist and have the temporary replaced with either a filling and/or crown. You could lose some of the root canal seal over time, which could cause the tooth to re-infect, so it is not something to put off very long.

Get it replaced: You shouldn't have pain, but you should call your dentist and get a new filling placed in the tooth to strengthen the tooth and help prevent the tooth fracturing. A new filling will also dover over the root canal and prevent new bacteria getting down to the tip of the root.

Either: Either the filling broke and the pieces fell out, or the tooth has decayed away from around the filling, allowing it to fall out. Please see your dentist now to resolve this issue before this small problem becomes a big one.