Exercise is key with or without a diet.
Bears repeating. I tried straight Atkins for three days, but I felt like crap and had a hard time with my runs. Modified it to include some carbs, and felt much better - and dropped pounds in short order.
Bottom line: find out what works for you, and what you can live with. Changes shouldn't be thought of as a diet plan at all. They should be easy enough to be permanent. Then you can still go home for the holidays and cram your face with pie... come home and get back into your routine and you'll be back in your pants in no time.
You were probably detoxifying, which can be uncomfortable, to say the least. Good for you. I am beginning to see that many people who don't appear to do well on an Atkins-style diet probably do not have the deranged sugar-metabolism problems that those who do well from the beginning almost always have. For instance, in my own case, I went from a blood pressure reading of 220/110 in less than three weeks on Atkins. But I had ALL the other symptoms of "Carbohydrate Poisoning."