I’ve been falling asleep suddenly during the day — what could be causing this?


I’m 40 years old and in good health. But lately I’ve been falling asleep suddenly during the day. What could be causing this?


I hope it’s not from reading my column. If it is, you’re not going to learn the answer to your question — because reading the answer will put you to sleep!

Seriously, there are many things that can cause a person to fall asleep suddenly. Your sudden bouts of sleep might be caused by a rapid drop in your blood sugar. They could be the side effect of a medication you’re taking, or could result from stress, depression or inadequate sleep at night.

Another possibility is narcolepsy. This disorder causes extreme daytime sleepiness and sudden episodes of deep sleep. Sleep can occur often and at inappropriate times, for example, when you’re talking, eating or driving. Narcolepsy usually appears much earlier in life, before age 30. Since you’re 40, narcolepsy is a possibility.

You say you’re falling asleep “suddenly.” If “suddenly” means, for example, that you feel sleepy after dinner, read the paper on the couch and find yourself nodding off as you read — that’s not narcolepsy. On the other hand, if you are eating dinner, and your head drops onto your plate and you’re sound asleep — that’s “suddenly,” and it could be narcolepsy. I’m not being humorous: People with narcolepsy fall asleep just that way.

More than half of people with narcolepsy also experience sudden episodes of muscle weakness where their whole body just collapses. It’s called cataplexy. And many with narcolepsy experience brief memory lapses or blackouts caused by very short periods of sleep.

To find out if you have narcolepsy, you’ll need a sleep study. This test measures your brain waves, eye movements, muscle activity, heartbeat, blood oxygen levels and breathing while you’re sleeping. It can help rule out other explanations that could account for your daytime sleepiness, such as sleep apnea.

A specific study, called a multiple sleep latency test, is also necessary to diagnose narcolepsy. This test is done after a good night’s sleep. It measures how quickly you fall asleep for a daytime nap, and also reveals whether and how quickly you enter rapid eye movement (REM) sleep during your nap.

If you have narcolepsy, it doesn’t mean you need more nighttime sleep. But regularly scheduled, short daytime naps are an important part of narcolepsy treatment.

Stimulant medications can help to relieve some daytime sleepiness. Modafinil (Provigil), armodafinil (Nuvigil), methylphenidate (Ritalin, others) and dextroamphetamine (Dexedrine) are stimulants commonly used to treat narcolepsy.

I’m sure this has occurred to you, but if you’re falling asleep without warning, don’t engage in any activities that could be dangerous if you unexpectedly lose control. That includes driving, and even smoking, because of the danger of falling asleep with a lit cigarette in your hand.