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Narcolepsy is a chronic disorder affecting the brain where regulation of sleep and wakefulness take place. Narcolepsy can be thought of as an intrusion of dreaming sleep (REM) into the waking state. 

The obvious reasons why a person should not be allowed to dive are as follows: 
--Disorders that lead to altered consciousness 
--Disorders that inhibit the "natural evolution of Boyle's Law" 
--Disorders that may lead to erratic and irresponsible behavior. 

Some people, no matter how much they sleep, continue to experience a irresistible need to sleep. People with narcolepsy can fall asleep while at work, talking, and driving a car for example. These "sleep attacks" can last from 30 seconds to more than 30 minutes. They may also experience periods of cataplexy (loss of muscle tone) ranging from a slight buckling at the knees to a complete, "rag doll" limpness throughout the body. 

The prevalence of narcolepsy has been calculated at about 0.03% of the general population, or, about one person in 2000. Its onset can occur at any time throughout life, but its peek onset is during the teen years. Narcolepsy has been found to be hereditary along with some environmental factors. Narcolepsy is a very disabling and under diagnosed illness: the effect of narcolepsy on its victims is devastating. 

Studies have shown that even treated narcoleptic patients are often markedly psychosocially impaired in the area of work, leisure, interpersonal relations, and are more prone to accidents. These effects are even more severe than the well-documented deleterious effects of epilepsy when similar criteria are used for comparison. 

Symptoms 
 Excessive sleepiness. 
 Temporary decrease or loss of muscle control, especially when getting excited. 
 Vivid dream-like images when drifting off to sleep or waking up. 
 Waking up unable to move or talk for a brief time. 

Narcolepsy and Driving 

There are several states that have imposed driving restrictions upon people with narcolepsy. These restrictions usually entail a narcolepsy-free period of one year after starting treatment; and, no drug-related symptoms. 

Another aspect of this condition concerns the side effects from the drugs used to combat the sleepiness. Medications used to treat narcolepsy include stimulants, anticataplectic compounds and hypnotic compounds, some of which have definite effects and side effects that are inimical to diving. Stimulants that increase the metabolic rate can cause an increased risk of oxygen toxicity in nitrox divers. Any of the drugs that alter the sensorium, alter the decision-making process or increase risk-taking are definitely adverse to divers. 

Here are some of the medications used to treat narcolepsy. 
Stimulants 
Methylphenidate-HCl, Ritalin®, RitalinSR® (extended release). Ritalin can cause joint pains, nervousness, abdominal discomfort, headache, dizziness, rapid heart palpitations and is used primarily for ADD. If this is the diagnosis, the person should not be diving. 
Dextroamphetamine-Sulfate: Dexedrine®, Dextrostat®, Dexedrine-SR®. These drugs can cause increased metabolic rate, blood pressure elevation and could increase the risk of oxygen toxicity. 
Methamphetamine-HCl: Desoxyn. Better distribution in the brain vs. the periphery, more potent and effective than amphetamine, used in the U.S. Same as above. 
Pemoline: Less potent and effective, long duration of action, hepatotoxicity 
Mazindol: Sanorex® Weakly effective, rarely used except in the U.K. 
Modafinil: Provigil®  Fewer sympathomimetic effects and side effects, long duration of action, well tolerated but lower potency than amphetamines. 

Anticataplectic Compounds 
Protriptyline: Triptil®, Vivactil®  Anticholinergic effects (dry mouth, blurred vision, constipation, etc.) at high doses, mild stimulant, preferentially adrenergic effects (mimics adrenalin) 
Imipramine: Janimine@, Tofranil®  Anticholinergic effects 
Desipramine: Norpramin®, Pertofran®  Same as imipramine but more adrenergic effects 
Clomipramine, Anafranil®  Very effective, mostly used in Europe 
Fluoxetine, Prozac®  Well tolerated but high doses are often needed, less weight gain than with other antidepressants, preferentially serotoninergic 

Hypnotic Compounds 
GammaHydroxybutyrate (under development with the name of XYREM®)   Short duration of action, resulting anticatapletic effects during daytime. Any decrease in alertness or sensorium is adverse to diving. 

Hypnotic Benzodiazepines   Same as for the treatment of non-narcoleptic insomnias. Decreased alertness adverse to diving. 

Advice About Diving

Whether or not a person with narcolepsy should be certified as 'fit to dive' should be decided on the merits of each case, the type of drugs required, the response to medication, and the length of time free of narcoleptic problems. Relationship to excitement, emotions and stressful situations should be taken into consideration. Prospective divers should in all cases provide full disclosure to the dive instructor and certifying agency - bearing in mind the safety of buddies, dive instructors, divemasters and other individuals who are always affected by diving incidents. It might also be wise to consider the use of a full face mask to decrease the risk of drowning in case of unconsciousness during a dive.