If i start a low carb diet after being off for 3 to 4 weeks, will my body have to go through that same "low energy" for those first two weeks again?

No: There is really no good reason to have low energy on a 'low carb' diet if your getting enough calories. I f you are on a protein sparing modified fast diet like optifast or medifast (very low calorie diets)you may experience some fatigue. Be sure you get enough good quality protein, adequate rest and some reasonable exercise. Low refined/white carb/sugar diets are healthy.