both headlights cut out

Hi there, I have a weird problem, both my headlights cut out for a short time and then suddenly go back on. I have just had a service and a pre-NCT (MOT) and it wasn't detected, though it has happened once or twice before. I had the battery replaced a couple of months ago and I don't think it happened before that, but it was summer so I'm not sure. Does anyone know what may be causing this? I drive a lot on minor bendy roads so it's really scary!!