I don't understand... where's the Snowman?

It's my fault, I thought too late to photograph it.

there's a recognised "disease" called Seasonal Affective Disorder (SAD)

Yes, I am aware of that. And I really think that prolonged cloudy weather affects a person's mood. You don't even need to do a lot of research here, it's self-explanatory to me. In good sunny weather, the mood is better, there is more energy, and the desire to work is much greater :-)