Why do rainy days make me tired?

Is this just a psychosomatic or psychological conditioning thing, or is there some confirmed scientific basis for it?

I got the same amount of sleep two nights ago and last night. Yesterday it was sunny out and I had the energy to work all day and evening. But today, it’s overcast and rainy, and I still have to work all day and night, but all I can think about is going back to sleep. I have noticed this correlation time and time again.

Thank you in advance.