These symptoms can be characteristic of dehydration, which can occur due to a number of different causes, although sweating would not be common in severe dehydration. Infections or low blood sugar may be other causes. Fatigue is a very common and nonspecific symptom that is seen in any number of conditions. Check in with your doctor if you are concerned about your symptoms.
While the list below can be considered as a guide to educate yourself about these conditions, this is not a substitute for a diagnosis from a health care provider. There are many other medical conditions that also can be associated with your symptoms and signs. Here are a number of those from MedicineNet:
Dehydration is the excessive loss of body water. There are a number of causes of dehydration including heat exposure, prolonged vigorous exercise, and some diseases of the gastrointestinal tract. Symptoms of dehydration include headache, lightheadedness, constipation, and bad breath. Treatment for dehydration is to replace lost fluids and electrolytes.
Infectious mononucleosis is a virus infection in which there is an increase of white blood cells that are mononuclear (with a single nucleus) "Mono" and "kissing disease" are popular terms for this very common illness caused by the Epstein-Barr virus (EBV).
Low blood sugar, or hypoglycemia, is a syndrome in which a person's blood sugar is dangerously low. People with type 1 and type 2 diabetes are at risk for this condition. There are other diseases that can cause a person's blood sugar levels to go too low, for example, pancreatitis, Cushing's syndrome, and pancreatic cancer. Symptoms and signs that your blood sugar levels are too low include palpitations, trembling, intense hunger, sweating, nervousness, and weakness. If your blood sugars become too low, use these nearby as a quick treatment table sugar, soda, juice, and glucose tablets.