I do same. First cup is regular. Then decaf rest of day.

For some reason, when I worked from home, I was getting a headache in the afternoon. All the time. Then one day I only got a chance to get my first cup of coffee. On that day, no headache. So upon further testing it turned out that I can only drink one regular cup when working from home. But on weekends or working from the office, this is not an issue. Only working from home.