The main room light was switched off. Bulb flashed on and there was a click similar to when a bulb blows - as usually happens when it's first switched on. Presumably when off at the light switch there should have been no power to the bulb so how could it flash on?
When these types of problems arise, the first thing to do is.
Safely isolate circuit and prove it is dead.
Then check your accessories light fittings and switches for loose connections.
Loose connection should then correctly terminated and grub screw tight.
If any arcing is evident, burning/black on conductor ends, this should be striped back to clean copper, if damage is also evident on accessories, replace them.