9 12 15 18 21 24 3 6 9 20 15 10 5 0 Alertness Level Multiple Sleep Latency T est (MSLT) Peak alertness Dangerously drowsy Time of Day 1-3 AM Reduced alertness Slightly impaired Figure 13-5.  Many human variables rise and fall daily due to one’s natural circadian rhythm.  If you find yourself suffering from acute fatigue, stay on the  ground. Glider pilots often become fatigued while flying  due to soaring in close proximity to other gliders in areas of  lift or because of the constant requirement to see and avoid  other traffic. Getting adequate rest is the only way to prevent  fatigue from occurring. You should avoid flying when you  have not had a full night’s rest, when you have been working  excessive hours, or have had an especially exhausting or  stressful day. If you suspect you are suffering from chronic  fatigue, consult your doctor. Hyperventilation occurs when you are experiencing  emotional stress, fright, or pain, and your breathing rate  and depth increase, although the carbon dioxide is already  at a reduced level in the blood. This can happen to both the  experienced and novice pilot. Hyperventilation causes an  excessive loss of carbon dioxide from your body, which  can lead to unconsciousness due to the respiratory system’s  overriding mechanism to regain control of breathing. Glider pilots who encounter extreme or unexpected  turbulence or strong areas of sink over rough terrain or water  may unconsciously increase their breathing rate. When flying  at higher altitudes, either with or without oxygen, a tendency  to breathe more rapidly than normal may occur, which can  lead to hyperventilation. It is important to know the symptoms of hyperventilation  and correctly treat for it.  [Figure 13-6]  Treatment for  hyperventilation involves restoring the proper carbon dioxide  level back in the body. Breathing normally is both the best  prevention and the best cure for hyperventilation. In addition  to slowing the breathing rate, you also can breathe into a paper  bag or talk aloud to over-come hyperventilation. Recovery is  usually rapid once the breathing rate is returned to normal. Gliders are not pressurized, therefore, pressure changes can  affect glider pilots that are flying at high altitudes. Inner ear  pain and a temporary reduction in ability to hear are caused  by the ascents and descents of the glider. The physiological  explanation for this discomfort is a difference between the  pressure of the air outside the body and the air inside the  middle ear. The middle ear cavity is small and located in the  bone of the skull. While the external ear canal is always at the  same pressure as the outside air, the pressure in the middle ear  often changes more slowly. Even a slight difference between  external pressure and middle ear pressure can cause discomfort. Headache Decreased reaction time Impaired judgment Euphoria Visual impairment Drowsiness Lightheaded or dizzy sensation Tingling in fingers and toes Numbness Pale, clammy appearance Muscle spasms Common Symptoms of Hyperventilation Figure 13-6.  Common symptoms of hyperventilation.  Inner Ear Discomfort Hyperventilation 13-5