Why have my headlights suddenly stopped working on my Toyota Aygo?

[Tonka 7]

I had a callout to work two nights ago in the early hours of the morning in heavy rain with some surface water. I have a Aygo on a 16 plate with 17,000 miles on the clock. The headlights were working when I left home. When I got to the part of the route with no streetlamps I realised I couldn't see the headlights has stopped working. The side lights were on front and back but no dipped beam and the high beam was OK too. Anyway later in the day I checked the lights and the headlights were all working again. I checked the fuse box in the engine compartment and the fuse box looks water tight. so that was a strange one. Has anyone else had this happen?