I cannot recall how many times the following scenario has happened.
I have been labouring on a task at my desk. My mind has got completely stuck after searching for a long time for a solution which has been eluding me. And then when I stand up and go for a drink or a trip to the toilet, an inspiration strikes like lightning.
I did not notice the amazing change at first, but I have had enough such experiences now to convince me that one thinks better while standing.
So get your bum off that chair - at least once in a while!