We are sorry to hear you have been feeling unwell.
The most likely reason for the lethargicness you are experiencing is due to your carbohydrate intake being much lower than usual. When carbohydrate intake is very low the body produces a by-product which can make some people feel a little nauseous or lethargic, so this can be common side effect during the first 3 days. This feeling should subside once in the Trimsition phase when the carbohydrate serve at dinner is introduced, and the amount of vegetables is increased. It is important to make sure you are drinking the recommended 2- 3L of water, and drinking this frequently throughout the day to help flush out the by-product that may be the cause of the lethargicness.
BT Nutritionist 🙂