In general, interrupted sleep is not as good as continuous sleep, but it can be quite adequate if you’re not awakened too many times, if you can fall back asleep quickly, and if you get enough sleep in total.

In the “siesta cultures,” people typically sleep six hours at night and two hours after lunch, and they do fine, said Dr. Gregory Belenky, director of the Sleep and Performance Research Center at Washington State University.

You can also feel and function just fine if you are wakened two or three times a night and get back to sleep easily. But if you need eight hours’ sleep and you actually get only five because of all the time you lose being awake in the wee hours, you may not feel restored and may feel irritable the next day, he said.

Worse than small children or prostate problems is obstructive sleep apnea, which awakens some sleepers every few minutes, making restorative sleep virtually impossible. Aging also can make people wake up several times at night, noted Belenky, who is 63 and copes with his awakenings by spending nine hours in bed to get eight hours of sleep.

But for people with genuine insomnia – those who have trouble falling asleep and get anxious if they wake up and can’t get back to sleep – spending extra time in bed is the wrong approach, said Cynthia Dorsey, an associate psychologist at McLean Hospital in Belmont and director of behavioral sleep medicine at the SleepHealth Centers, a chain of for-profit sleep labs affiliated with the Harvard teaching hospitals.

For them, she said, what often works best is to restrict time in bed to reduce the time you spend awake and fretting. It’s better, she said, to read or do some other quiet activity until you are genuinely sleepy, and get out of bed and read again if you can’t sleep. If kids do wake you up at night, she said, you can practice some cognitive-behavioral therapy techniques such as not telling yourself you will never get back to sleep but instead say, “That’s not a foregone conclusion. That may not be true tonight.” Above all, she said, don’t try too hard to sleep: that is counterproductive.