There are many beliefs about sleep, but not much verified knowledge. For instance, it is not true that one hour of sleep before midnight is worth two after.
It is true that a lot of fatigue is due to mental processes, rather than physical fatigue.
We are probably all underslept, since most adults have trouble getting "catch-up" sleep. When you were in high school or college, you could probably make up for the sleep deficit you incurred during the week by sleeping till noon or later on weekends. As we get older, we seem to lose this ability, while at the same time we awaken at night more frequently.
As a physician, I observe that my chronically underslept patients are more irritable, with degraded ego functions as well as more muscular pains and aches, and have some degree of depression. They also seem to function closer to baseline when doing well-known and repetitive tasks, but have trouble concentrating on crossword puzzles and the like. (Or as we used to say as interns, we could run a cardiac arrest with no sleep, but it was difficult to do an intake interview.)
Another danger of being underslept is falling asleep behind the wheel of your car, or making other errors. The government recognizes this by putting a limit on the number of consecutive hours a truck driver can drive, or a pilot can fly. The number of hours a medical intern can be on call at a hospital is also limited, but strangely enough a 60-year-old medical attending has no limits placed on his hours. In fact, if a patient called me at 10 at night and I told him/her that instead of getting my advice, because I had been awake for 16 hours ,they should go to the nearest emergency room where they could be seen by a well-rested doctor, they would be very upset.
Since lack of sleep is so corrosive and destructive, both mentally and physically, I see nothing wrong with the use of sleeping pills. I would prefer the use of sleeping pills to a patient falling asleep at the wheel of his/her car. Some patients are concerned about becoming dependent on sleeping pills, but I believe that many adults have "irritable sleep syndrome" and need some chemical help to get sufficient sleep.
Sleep apnea studies are in a curious position. They are reviewed by psychiatrists, neurologists, pulmonologists, and ENT doctors. The definition of sleep apnea is somewhat imprecise. (If you are not an overweight male who snores, the chance of your having sleep apnea is greatly lessened.) We all have apneas, generally defined as cessation of breathing for 10 or more seconds. The diagnosis is firmer if the oxygen saturation drops below 85% at the same time. There are also hypopneas, which are episodes of underbreathing without complete cessation. We have also known for a long time that everyone drops oxygen saturation during sleep, which is why we put nasal oxygen on all heart attack patients. Oxygen desaturation is a potent pulmonary artery vasoconstrictor, which overloads the right ventricle, which can tolerate volume overload better than pressure overload.
Since the number of apneas increases with age, the definition of sleep apnea depends in part on a patient's age. My two additional criticisms of all sleep apnea studies are:(1) no one asks the patient (usually a male) if he would be willing to wear a positive pressure sleep mask for the rest of his life, and (2) it would be more efficient to put a patient suspected of sleep apnea on a CPAP and then a BIPAP mask to see if they felt less tired, etc. the next day, but insurance and Medicare only pay for the mask if you first diagnose sleep apnea. In other words, unlike putting a patient on an antidepressant, CPAP cannot be used as a diagnostic/therapeutic treatment and test.
Before I send a chronically fatigued patient for a sleep apnea test, I try one month of Prozac or other SSRI, then one month on Effexor XR or Wellbutrin SR, and finally one month on Provigil, which is FDA approved for CNS stimulation of patients with sleep-shift disorder or chronic insomnia/fatigue, and seems to have no ischemic cardiac effects.