DEAR DOCTOR K: 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?
DEAR READER: 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.
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.
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 sleep during your nap.