Chances are you are already productive. So, an anecdote:

I noticed that when I make lists of things to do, and I see progress on the items ticked off, I know I am productive. No anxiety after that. (I usually write down the number of hours taken to complete each task and sometimes flip through the list to reassure myself with indulgent self-adulation).

Without the list, even though I am killing items, I still feel unproductive. It's that bizarre.

Make a list! :-)