Hi, I feel the same. When I am tired, I get to a point in the day (usually when most are going home) that I can get into a flow state. I get through the work, there are few interruptions and I can work far more productively. There comes a point though where I tip over into just too tired, usually after working this way all week.
Another strange observation for me was when I used to have a hangover (I don’t drink much anymore). Usually the day after a work party my day would start like my colleagues with a foggy brain and needing a toastie, but as the day went on I would spark up and go on to do some of my most focussed work and be working long after everyone else had gone home to rest. Thus partly due to the sleep deprivation I’m sure!
My anecdotes are all while on medication.
We are not alone! 😊