I have been doing Atkins, or variation of, for more than a year. Both my husband and I have lost a substantial amount of weight and we feel great. My cholesterol levels have gone down and so has my BP.
However, I will tell you that when I first began Atkins, I felt awful. I had a headache that would not quit for days and just felt all around cr***y. This eventually went away and I began to feel a lot better, but some others on Atkins have reported the same. Doesn't happen to everyone, but if you are feeling lousy --- stay with it. You are in withdrawal and things do get a lot better. It is worth the bit of pain, for the wonderful results.
It's ugly and it's painful, but you'll live (you may not feel like you want to, though), and it should only last a few days, at the most. It's a killer going without the morning pot of coffee. I DON'T recommend treating the headaches with aspirin or Tylenol, just drink water. Helps flush the system.