Yes, it’s normal. There are two processes: getting into ketosis, and fat- (or keto-) adaptation. The former happens very quickly, the latter takes weeks.
All it takes to get into ketosis is a low enough insulin level, and that is achieved by dropping the carb intake. How low carb intake has to go for someone depends on how insulin-resistant that person is, since the greater the insulin-resistance, the greater the insulin response will be to a given stimulus. (It is possible to regain insulin-sensitivity over time, but it won’t happen overnight, which is why we caution people not to be too eager to increase their carb intake too soon in the process.) But once insulin drops below a certain threshold, the liver begins manufacturing ketone bodies and what little glucose the body actually needs.
Fat-adaptation takes longer, generally six to eight weeks in most cases. During this period, athletes will notice a drop in performance. The reason is that skeletal muscles are being deprived of their accustomed fuel, glucose, and haven’t yet re-adapted to metabolising fatty acids, so in the meantime, they are limping along on ketones. The reason fat-adaptation takes time is two-fold: first, the mitochondria in the muscle cells have been damaged from years of metabolising glucose. They need time to heal and make healthy baby mitochondria. Second, there are other cellular pathways involved in metabolising fats, which have been deactivated from lack of use, and they need to be reactivated. Once the muscles have readapted to metabolising fatty acids, they will actually pass up glucose and ketones in favour of fatty acids, a state called variously “physiological insulin-resistance” or “adaptative glucose-sparing.”
All this takes a certain amount of time. You will notice your energy level rising again over the next few weeks, but in the meantime, go easy on the exercise. By the time you are fully fat-adapted, your endurance will be back at, or possibly better than, its pre-keto levels. Explosive power will take somewhat longer to return, but it, too, will eventually be as good as ever.