Summertime is so relaxing, what with its casual schedule, the warm weather that draws folks outdoors late into the evening, the promise of vacation respite and fun. And all of that restful sleep.
Except when you can't get to sleep. Or you crash, but you can't stay asleep.
"Summer is really fraught with sleep hazards," psychologist and author Michael Breus says.
Right about now, some people are realizing that the season isn't the reprieve they envisioned, and few things are more frustrating than summer sleep problems.
"It's the heat," says Sue Sykes Berry of Kansas City, Mo., who has trouble sleeping when her house won't cool down at night. "Then there's the dog and cat that want to sleep with me, even if it's 100 degrees."
She's right about the heat, and there's good science to back her up. Humans tend to sleep best when the ambient temperature is 65 to 75 degrees.
That's bad news for Darnell Williams of Kansas City, Kan., whose older apartment has window air conditioners without thermostats. He and his wife have the added task of trying to keep their 6-month-old comfortable.
"Either you wake up freezing to death, or you wake up a sweaty mess," Williams says. "It's just bloody murder."
Hot nights aren't alone in disrupting sleep. And you are far from alone if the summer months bring more tossing and turning than rejuvenation. Breus says the numbers go up in his sleep lab during the summer.
Knowing the causes of summer sleep problems can help point to corrections, sleep experts say.
"Almost any change of the environment has some degree of effect on sleep quality," says Damien Stevens, a physician who specializes in sleep medicine at the University of Kansas Hospital.
And you can be a victim of disrupted sleep -- the bane of high-quality sleep -- without even knowing it, Stevens says. Unless you're awake for several minutes, you won't recall the disruption.
Much shorter wakeful periods can occur -- three seconds each, say -- but those are enough to reduce sleep quality.
So, what are the worst troublemakers?
First, the heat. People fall asleep as their body temperature falls, and they wake up in the morning when body temperature rises.
But all during the night, as the body goes into "rapid eye movement" sleep, it periodically loses the ability to sweat and shiver, says Ann M. Romaker, medical director of St. Luke's Health System's Sleep Disorders Centers.
Body temperature starts to match the surrounding air temperature. The result can be numerous waking episodes.
There's evidence that people native to very hot climates are acclimated to sleeping in higher temperatures, Stevens says. The rest of us aren't that lucky.
So, a tough fix? Definitely.
If your air conditioner is struggling, adding a fan can help. A breeze on the skin increases evaporation, cooling the body. (Leaving the fan on when you're not in the room mostly wastes electricity.)
Breus, whose books are "Good Night" and "The Sleep Doctor's Diet Plan," says to pay attention to the "microclimate" in the bed. Even weighty sheets can increase temperature.
Some people seek assistance with specialty products such as the Chillow, which is made from "thermoregulating" material that stays cool and is placed on top of the pillow.
Sykes Berry plans to try one. As it is, she resorts to sleeping pills when it's very hot.
"That's not optimal, I know, but at least I get some sleep," she says.
Many people report they have "pent-up energy" after exercise, and that delays restfulness, Stevens says, so it's a good idea to end workouts two hours before going to bed. Some people need four or even six hours between exercise and bedtime.
Summertime means crowded bar patios late at night and evening runs for ice cream and "fourth meals," even during the week. Experts say the effects of food and alcohol on sleep are often misunderstood.
Alcohol acts as a sedative at first, helping people fall asleep. But later during the night, the effect is reversed, causing episodes of wakefulness and low-quality sleep. Romaker recommends no alcohol in the two hours before going to bed.
Late eating can be a minus for weight maintenance, and it also can disturb sleep, especially for those with acid reflux problems. A good guideline is to stop eating two hours before going to bed, Romaker says.
"You should never go to bed hungry," Breus says, "but you should be careful how much you ingest late. The body was not meant to digest food lying down."