Reducing your carbohydrates allows you to enter the dietary state of ketosis, where you primarily burn fat for energy instead of sugar. This requires you to severely limit your carbohydrate intake and avoid all sugars. Diets of this sort present certain difficulties, including a lack of energy if you typically run on a high-carbohydrate diet. Consult a health care professional before beginning any diet or exercise program.
Low-carbohydrate dieting limits your body's ability to use glycogen for energy. The more you restrict your carbohydrates, and the more you are physically active, the quicker you will experience a loss of energy. Over time, your body becomes more accustomed to running primarily on ketones, free-floating fatty acids, instead of sugar, but it takes a while to adapt to this. If you are following the Atkins diet or a similar variation, this is usually dealt with during a two-week period known as the induction phase.
Sleepiness can be the direct result of a lack of energy. Even though you are dieting, if you cut your calories too far, you may be suffering from a lack of total energy to work with. Regardless of the type of diet, excessive caloric restriction can result in both sleeplessness and sleepiness. Until you become accustomed to running on ketones, you may experience sleepiness or euphoria, a dazed feeling, as your body becomes accustomed to having less sugar and more fat to run on.
You may sweat more on a low-carbohydrate diet for more than one reason. As your glycogen, or sugar levels deplete, you lose your ability to store water. Each gram of stored glycogen retains 4 g of water. As you must consume as much or more water while dieting than you did before you started your diet, you are going to expel water quickly, and some of this may be via sweating. At night, you may still have ketones to burn, and burning this form of energy can raise your temperature slightly in a rested state. This may also cause a slight increase in sweating at night.
Energy and Sleep
To ensure that your energy levels are high enough, make sure you are eating enough calories, and enough of the right foods. Even though you are limiting your carbohydrates, do not make up for this by eating saturated fats. Healthy fats such as those found in olives and olive oil, fish, nuts and seeds are all burned more efficiently than saturated fats. As you become accustomed to running on health fats, your energy levels should increase, as well as your ability to sleep.