There is also some promising research being done on sleep in adults, relating to focus, memory and cognitive performance. A study published in February in the journal Nature Neuroscience found that the amount of delta sleep in seniors correlates with performance on memory tests. And a study published three years ago in Sleep found that while subjects who were deprived of sleep didn’t necessarily report feeling sleepier, their cognitive performance declined in proportion to their sleep deprivation and continued to worsen over five nights of sleep restriction.

As it happens, “moves about excessively during sleep” was once listed as a symptom of attention-deficit disorder in the Diagnostic and Statistical Manual of Mental Disorders. That version of the manual, published in 1980, was the first to name the disorder. When the term A.D.H.D., reflecting the addition of hyperactivity, appeared in 1987, the diagnostic criteria no longer included trouble sleeping. The authors said there was not enough evidence to support keeping it in.

But what if doctors, before diagnosing A.D.H.D. in their patients, did have to find evidence of a sleep disorder? Psychiatric researchers typically don’t have access to the equipment or expertise needed to evaluate sleep issues. It’s tricky to ask patients to keep sleep logs or to send them for expensive overnight sleep studies, which can involve complicated equipment like surface electrodes to measure brain and muscle activity; abdominal belts to record breathing; “pulse oximeters” to measure blood oxygen levels; even snore microphones. (And getting a sleep study approved by an insurance company is by no means guaranteed.) As it stands, A.D.H.D. can be diagnosed with only an office interview.

Sometimes my patients have resisted my referrals for sleep testing, since everything they have read (often through direct-to-consumer marketing by drug companies) identifies A.D.H.D. as the culprit. People don’t like to hear that they may have a different, stranger-sounding problem that can’t be fixed with a pill — though this often changes once patients see the results of their sleep studies.

Beyond my day job, I have a personal interest in A.D.H.D. and sleep disorders. Beginning in college and for nearly a decade, I struggled with profound cognitive lethargy and difficulty focusing, a daily nap habit and weekend sleep addiction. I got through my medical school exams only by the grace of good memorization skills and the fact that ephedra was still a legal supplement.

I was misdiagnosed with various maladies, including A.D.H.D. Then I underwent two sleep studies and, finally, was found to have an atypical form of narcolepsy. This was a shock to me, because I had never fallen asleep while eating or talking. But, it turned out, over 40 percent of my night was spent in REM sleep — or “dreaming sleep,” which normally occurs only intermittently throughout the night — while just 5 percent was spent in delta sleep, the rejuvenating kind. I was sleeping 8 to 10 hours a night, but I still had a profound delta sleep deficit.

It took some trial and error, but with the proper treatment, my cognitive problems came to an end. Today I eat well and respect my unique sleep needs instead of trying to suppress them. I also take two medications: a stimulant for narcolepsy and, at bedtime, an S.N.R.I. (or serotonin-norepinephrine reuptake inhibitor) antidepressant — an off-label treatment that curtails REM sleep and helps increase delta sleep. Now I wake up without an alarm, and my daytime focus is remarkably improved. My recovery has been amazing (though my wife would argue that weekend mornings are still tough — she picks up the slack with our two kids).