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.