I would say it is absolutely possible for you to catch a cold, flu etc. etc. while fasting. You may be particularly vulnerable, being in the middle of removing old wastes and toxins and your immune system at a low point.
From my experience it is far better to fast through any crisis than it would be to break your fast and put your body back in the business of digestion while attempting to continue to detox and heal. I would fast through, do what it sounds like you're doing (flush flush flush!!), lay low, take special care of yourself and help your body take out that trash!
One of the reasons I did my extra long cleanse last summer was because I got The Bug big time the previous December. It went into my lungs, and I was still expelling mucous in MAY!! Scary.
I firmly believe what my dear naturopath tells me, that all my problems come from my intestines. I am still working diligently on colon cleansing, and went right back to that to remove the excess mucous from my body and prevent future trouble. This flu season I have had not so much as a sniffle!
Excess mucous is one of the Seven Warning Signs of Trouble! Any time you have mucous in your head, your intestines, your lungs... women can have it vaginally... this is a sign you should do some cleansing and detoxing. After the holidays I noticed a bit, did a short fast including cayenne and voila! Gone!
Yep, internal cleansing is work!! But speaking from my experience, it has been well worth all the effort. I will make it a part of my life, and know I can AVOID many illnesses, aches and pains and health crises. I like Paavo Airola's advice to fast one day per week, three days per month and ten days twice a year for maintenance. And of course with pre-cleanse and post-cleanse diet, that adds up to some healthy input, on a very regular basis!
Hope you are feeling better! Let us know how you are doing, and know we are thinking of you!