I had an electric fired in my bathroom last night. Now am experiencing sore throat, cough, nausea and tiredness. What could be the cause?

Smoke inhalation. If you had a fire smoke must have been produced. Therefore you may symptoms of smoke inhalation.See a doctor if symptoms persist.
Air quality issues. An electrical fire in your living space likely released a collection of smoke & fume particles that may still be cycling through your living space. If you haven't already, you should air out the space.A small particle or ionic air filter may help scrub the air. Such small particles can produce all the symptoms you mention & they may hang on for days.
Viral syndrome! Not sure what a "electric fired" means! but it sounds like you have a viral syndrome (upper respiratory infection). If you mean fire, it may be allergic or upper respiratory affects from inhalation. See a doctor.