What type of downlight is it?
LED Lamp, LED enclosed fitting? Low voltage, mains voltage?
It could be anything from a loose connection to an overheating lamp, or just a failure over time.its likes
Have the lights or switch been changed?
So nothing has been changed or replaced and it was working fine?
Sparky.Is it still under warranty? Some may have over a year on them.
Were they diy installed, or through an electrician?
Yeah I'll do that.Do the obvious and check for lose connections.