I don't know about after a joint injection, but those are definitely effects I recognize from when I've had cortisone intravenously to knock back intestinal inflammations. Almost a side "benefit" of the cortisone. Last time I had a cortisone treatment the doctor advised me to make the most of it by working out more once I was out of hospital. I'd be feeling energized for the few weeks I was scaling back down on oral cortisone, and "investing" that energy in more exercize would give a lasting benefit plus help counteract the bad side effects of sleeplessness and weight gain.