I quit sugar and flour all at once over 3 years ago and have not touched them since. I do eat fruit and whole grains though...and stevia for a sweetener. Sugar and flour are toxic and when you detox you can have flu like symptoms and your body will scream for you to give it what you are depriving it of...just like cigarettes or other addictive substances. Eating them will make the symptoms temporarily go away, but no, I don't think that you need to keep them in your diet and I strongly urge you not to.
Yes you can detox too quickly and if you are, you may need help. A sign of too quickly is being constipated...your body isn't able to keep up with everything being dumped. In that case you may want to look into colon hydrotherapy/colonics...it gets it out quick...or perhaps a juice fast...refer to Benefits of natural detoxification.I have also had colonics...a little shocking to hear about...but definitely worth looking into. When I was very toxic and overweight I had a series of them done and believe that it helped me very much. I have still had temporary flu like symptoms doing the juice fast like being tired, sweating, nausea, etc., but not since I gave up aspartame...I was eating so much of it that when I quit I got very sick...but it was followed by a great feeling of renewal...the flu like symptoms lasted about 1 1/2 days...normally I feel very clean and energetic on a juice fast because I'm getting all of the nutrition without the work of digestion...and it cleans out any stuck debris. According to Dr. Don Colbert, it's important to not water fast but to juice fast so that your colon stays active in ridding the body of the toxins...it works great for me.
I am not a doctor and these are just my opinions based on personal experience...you need to do what is best for you. I'm sure though that it is not bad for your health to give up sugar and flour completely....it's great for your health, the stuff is poison. If you are in question of anything though, go see your doctor. I am pro natural and pro preventive health, I think we need to stay on top of our health and be very aware of what our bodies are doing, but I still see a family DO, (Osteopathic Medical Doctor) when I have a concern and for regular check ups.