I was inside and caught the light out the corner of my eye and had time to turn and watch it continue downwards. There's reflection on the inside of the window - enough that I couldn't see if the stars were out until I went outside. I'm used to observing meteor showers, satellites and the ISS and am confident it was none of these things - it was quicker than anything like that. It was also definitely outside rather than something inside reflecting on the window.
