On Monday I was in a warm room in a happy mood and feeling fine. I managed 500 words. Yesterday I was in a foul mood, with a headache and the room was so cold I was sitting and typing with a duvet round me. I managed just under 4,000 words. And some of those four thousand words were definitely in the right order.
Today is lovely and sunny but cold, and I am next to a south facing window. Finger's crossed for a few thousand more words. I would rather be productive in comfort.