I've been doing ketosis diets the last few weeks. I have had 2 carb ups but only once felt zapped of energy and that was because I was on a cross trainer. I think it is because maybe your calorie and fat levels are too low. Remember, if you are on this kind of diet you have to eat very frequently. I work out 7 days a week and do cardio 7 days a week. Heres how my diet usually looks, or something like this
Meal 1
4-6 eggs scrambelled with about 1/8th a cup of butter, 2 hamburgers chopped up in it, 125 grams of turkey, table spoon of peanut butter
Meal 2
4 Hard boiled eggs, 125 grams of turkey, low fat jello
Meal 3
3 Eggs, 4 hot dog weiners
Meal 4
2 Eggs, 6 sausage links
Meal 5
2 Cans of Tuna mixed w/ Mayonaise, Table spoon of peanut butter
I usually use Xenadrine too but I ran out, (DON'T ORDER FROM BODYBUILDING.COM, MY ORDER IS TAKING WAAAAAAY LONGER THAN THEY SAY IT WILL). I usually just take 1 pill before my workout session and that keeps me going till bed time. If you are feeling extremely zapped, try taking a caffine pill. I have to do that every now and then and those also work great. Multi-vitamins too. Good Luck