What was the “Poof” sensation you felt on that day? My first, and hopefully last, PE injury sounds alot similar to yours. There I am jelqing and all of a sudden a sharp pain just underneath the head of the penis. I think the initial pain and shock is what caused your penis to become flacid again. As for not being able to get an erection, it’s best to stay away from all sexual activity for a month. When I had a similar injury all I could think about for the first week was the pain and depression I was going through. However stay positive, I decided to spend alot more time working out in the gym as this helped take my mind off the problem and after 2 weeks I was starting to get morning wood again (oh what a relief that was!) and by week 3 I was pretty much back to normal but didn’t start PE’ing again for a good 3 months.
Find something to take your mind off the problem, and whilst your enjoying your life your penis will heal itself. Like your doctor said, the majority of your problem is coming from worrying about your injury too much, just relax, take some time off whilst your penis recovers. STAY POSITIVE! Good luck hopefully this helped you out a bit.