I just got back from my annual 5 day backpacking trip and on the last day, I managed to get part of my sleeping bag stuck in the zipper and it tore! I knew if I left it, all the down stuffing would come out and there would be feathers everywhere! Fortunately, the fix was very simple, all you need is a sleeping pad patch!
Step 1: Locate the hole
If you have feathers flying out of your sleeping bag, this might be more difficult. Fortunately, I was able to fix the tear right after it happened, so I didn't have to spend hours combing over every inch of my sleeping bag. I've had to do that before and it's a huge pain. Shove as many feathers back inside as possible and then smooth out as many wrinkles as you can.