Hi there,
Are you taking any supplements?
If you mean you feel dizzyish and weak, you might need some potassium.
When we first eat low carb, we naturally lose a lot of excess water, and this diuresis tends to flush out extra potassium.
If you are not already taking a potassium supplement, I would suggest you add some. You'll need about 400mg at first, decreasing to 100mg as time goes on.
You can get tablets, or you can use potassium salt, Nu Salt or No Salt, available with the ordinary salt at your supermarket.
Do take the tablets with your meals, otherwise they may irritate your stomach. Also, make sure you are drinking lots of water.
And lastly, a warning. Check with your pharmacist first if you are taking medications for high blood pressure or diuretics.
I hope you feel a bit more energetic soon!
Rosebud