If a filling has fallen out it could be that:
the tooth is decayed and the filling was no longer held securely.
the filling itself has broken.
the tooth has broken or chipped and is no longer able to hold the filling in place.
a typical broken tooth/ lost filling situation
Control any pain with your regular painkillers and contact us for diagnosis and repair BUT if you are unable to attend straight away then you can buy temporary filling kits from most pharmacies which will plug the hole until you can seek proper treatment.