This seems odd. I've never felt better whilst doing a low-carb / ketogenic diet. I always feel great, and typically keep carbs to 10-20g per day max, only carbing up on the weekend.
My workouts while doing CKD's are typically 3 fullbody workouts per week, so they are fairly intense too. Maybe you need to increase your fat intake. Ketosis gives me great energy all day long, once my body has switched to fat burning mode for fuel. In my experience, only the first week should be a bit tough, but with nutrient partitioners to keep blood glucose levels down, it's very easy and fast to get into ketosis once switching to a low carb diet. I can usually do it within a week, and once I'm in --- very smooth energy all day long with no peaks and valleys. Just awake and alert all day, and workouts are pretty decent. I just have BCAAs around my workouts and I'm golden.