I chose to work!
I guess, having the choice whether you want to work or have a lazy day is a good thing. I chose to work in the bramble jungle. Grabbed the weed-eater and the power saw and started cutting into the wildly growing raspberry jungle.
Because of the cold weather I had put on a woolen hat, a sweater AND a warm jacket. Pretty soon I found out I was dressed way too warm. At lunch time I had exhausted myself to a point that I was ready for bed. Instead we had a power lunch and after an appropriate break I was ready for the second round. That round pretty much ended with a knock-out. Raking all the cut-off stuff together, carrying pieces of brushwood and swinging the weed-eater back and forth was too much for the first day of activity. I grudgingly acknowledge that 5 months in the South with almost no physical activity is a set-back for physical strength.
So next time, I have to be a bit more cautious with what activity I start outside.