I get the same and I only have coffee first thing in the morning. Redbush tea rest of the day.
It’s something that started in last few years (mid 40s). Though it mostly happens on days I’m in the office and I suspect it’s just tedium. When working from home I mix up the day with a variety of things, bits of work, house stuff, bike fettling even, more work. Day is spread out, I can get more done (unless it’s really tedious work I’d rather not do) and don’t tend to snooze in the afternoon.
Though it’s probably good to snooze in the afternoon anyway. Think we Brits should be more into siestas but we hate Europe so can’t be doing with foreign ideas like that. Plus it’s connected with warm weather, which we’re not blessed with.