Insufficient Sleep

• Tiredness is commonly caused by insufficient sleep, which also can cause brain fog. Naps can reduce fatigue from sleep deprivation, but people need a daily uninterrupted session of sleep that lasts six hours.
  
  

Other Factors

• Tiredness and brain fog can be the result of alcohol or drug use, stress, low carbohydrates, dehydration, excessive exercise, alcohol withdrawal, ingesting poisons or unsafe amounts of certain compounds, such as aspirin.
  
  

Prescription Drugs

• Tiredness and brain fog can be the side effects of prescribed medications or the interactions of multiple drugs.
  
  

Medical Conditions

• Tiredness and brain fog can be caused by head injury, heat stroke, low blood sugar, brain infection, diabetes, congestive heart failure, cancer, fibromyalgia, ADD, ADHD, depression, anxiety disorders and many other diseases that sap the body's energy.
  
  

Lack of Carbs

• Carbohydrates provide the body's energy. The brain needs an enormous amount of energy, so it's keenly affected by low carbohydrates. Low carbohydrates are sometimes a consequence of special diets, such as the Atkins Diet.
  
  

Medical Help

• If fatigue and brain fog persist after changes in behavior and diet, see a doctor as soon as possible.