Longtime lurker here. I haven't seen too many personal accounts of receiving the J&J shot here so I thought I'd share mine as thanks for all the Covid information I've gotten here and found so useful over the last year.
I have terrible medical anxiety so I specifically sought out the J&J due to the "one and done" factor. I received the shot Tuesday afternoon. I ended up leaving the recovery chair area after a minute or two, because I knew if I continued sitting in there I would pass out. I finished out my recovery period in the car, laying down, AC blasting, and I was fine. By evening I was definitely feeling more tired than normal and headed off to bed a little early. The next day (yesterday) I woke up feeling like I was at the tail end of the flu. Headache, muscles and joint aching, no appetite. I spent most of the day in bed alternately reading and napping. By 8pm my fever had broken and I could tell the corner had been turned. Today I feel absolutely fine and grateful to be fully vaccinated.