This is called the “keto flu” and is a known side effect of going through carbohydrate withdrawal. The same symptoms can also occur from electrolyte imbalance, which is why it's so important to consume adequate amounts of Himalayan sea salt to mitigate the symptoms. For most, these symptoms do not last long and subside as the body begins to adapt. In addition to Himalayan sea salt, homemade bone broth is another great option to help restore electrolyte balance. You can also purchase pre-made bone broth from your local grocery or health food store. Bone broth also heals the gut, so it can be a great asset to your health even if you are not dealing with an electrolyte imbalance.
Another option you can choose is to slowly transition your diet into less carbs and more fat, which should reduce the risk of symptoms. Please note that this gradual approach will slow your adaptation into ketosis.