According to Dr. Atkins

During Induction, a small percentage of people get withdrawal symptoms, which may include headaches, nausea, dizziness, fatigue, muscle cramps or irritability. If this happens to you, increase your intake of vegetables for several days. But as soon as your withdrawal symptoms have abated, go back to consuming no more than 20 grams of carbohydrates a day. Withdrawal rarely lasts more than four or five days. Or, if your weight continues to come off, you may stay at that level until you are ready to move to a higher level of carb consumption and slow down your weight loss. If you can ride out the symptoms, they should disappear within four or five days. Be sure you are drinking enough water and take a supplement that contains magnesium, calcium and potassium.
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If you're planing on going back to being a vegetarian, spare yourself the pain of induction and forget about Atkins or most low-carb diets. You'll be missing too many nutriments by that can only be found in meat and fish, which is required in this way of eating.