I have a similer thing happen but it usualy stops by day 3. I’d see it as a good part of the healing process though. Could be some form of detoxification. Your not eating or drinking to create this mucus but its leaving you, so it must be built up in you from before you began dry fasting or its been created by your body during the DF as a trasport system to get toxins out of you. From my experience It’ll stop eventualy and you’ll feel better and your air ways will be more open once its gone. Congrats on day 4! 11 days is pro level fasting in my books. Goodluck