THE HUMAN CONDITION: BEDSIDE MANNERS : The Sleep Wars : He’s hot. She’s cold. He likes a firm mattress. She likes a soft one. No sweet dreams for them.

It wasn’t until after they were married that Karen’s husband found out about her bedtime, er, companions.

The intruders were named Willow, Dillow, Sillow and Pillow--small, feathery pillows that were family heirlooms. They had been with her since childhood (she even took Willow and Dillow overseas on her diplomatic missions), so Karen saw no reason not to include them in the marriage.

But when two sets of bedtime habits vow to become one, the results aren’t always sweet dreams.

“He didn’t really know the pillows existed until our honeymoon,” recalls Karen, who lives in Omaha. “And then when he found out they had names. . . . I don’t think he thought I was real.”

Her husband adjusted. After five years, he can even identify Willow and Pillow, Karen reports. Now, the couple sleeps relatively well.

For other couples, bedtime difficulties aren’t resolved so smoothly.

He’s hot. She’s cold.

He likes a firm mattress. She likes a feathery one.

He sleeps nude. She wears flannels.

He falls into bed at midnight, ready for sleep. She climbs in, turns on the lamp and reads for an hour.

You and your significant other may share a love of sailing, Woody Allen movies and Chinese food, but sleep is a very individual thing. Disagreements over mattresses, room temperature, what you wear (or don’t) and which side of the bed you claim all have the potential for making a relationship go bump in the night.

For some couples, resolving the bedroom’s temperature is like trying to compromise between a vacation in Hawaii and one in Alaska.

It’s not that most don’t try.

Irene admitted that she has had a hard time adjusting to her husband’s thermostat. While some, like Irene, like it hot, he liked it cold. The Buffalo couple thought they had found the perfect solution in an electric blanket with dual controls. Still, she froze and he roasted. Seems the individual controls work better when the blanket has not been put on the bed upside down.

The sleep wars.

They are, says one observer, “the stuff marriages are made and broken on.”

Adds another veteran of the spousal sleep skirmishes: “There should be sleep counseling. I mean, we have marriage counseling, right?”

Hmmm. Sleep counseling. Sort of a marriage counseling for the unconscious hours.

Sleep disorder experts say bedtime incompatibility can cause serious health problems, even marital woes.

“Studies show people, by and large, sleep better alone than with someone in the same bed,” says Dr. Phil Westbrook, director of the sleep disorders center at Cedars-Sinai Medical Center. “But people think they have made that marriage commitment, and part of the commitment means they have to sleep together. And if they don’t sleep together, something has failed.”

How a couple adapts to each other’s sleeping style could be a reflection on the marriage, says Dr. Gary Richardson, director of the Sleep-Wake Disorders Clinic at Brigham and Women’s Hospital in Boston.

Bedtime, he says, “is an arena where compromise, conflict and adjustments end up being played out rather than at other times of the day.”

Before Barb’s marriage broke up, she and her husband regularly argued about their conflicting bedtime habits.

“We had a terrible arrangement,” says the Los Angeles woman. “But I just felt I had to grin and bear it.”

He liked the window open. She liked it closed. She liked covers. He did not.

Another snag was wake-up time.

“It was the bane of my existence. He’d get up at 4:30, and I wouldn’t have to get up until 6,” she says. Dual alarm clocks solved the problem, but “it took a whole year for me to learn to sleep through his alarm.”

But rock bottom, as for many other couples, was his snoring.

Studies show that women are lighter sleepers and more likely to be awakened by their partners’ movements. In addition, more men snore. (It’s a fact.) For instance, 60% of men over age 60 snore, compared to 40% of women in that age group, according to the Better Sleep Council.

And if you don’t think snoring can cause loss of sleep, consider this: The highest recorded decibel level of snoring is 90, comparable to heavy traffic or thunder and just under the noise level of a jet taking off.

“I was coming to work like a zombie because of his snoring,” says Barb. “Finally, I told him he had to do something about it or sleep on the couch. You just can’t sleep through earth-shattering snoring. I don’t know how women stay married to men who snore.”

According to Westbrook, snoring can be alleviated with professional help. But other problems may require separate beds.

“Sometimes the solution is not to sleep together, to get two beds in the same room,” he says. “The critical thing is that people get enough sleep. Not sleeping is not an option. That’s dangerous to one’s health.”

And to one’s marriage.

Raise the topic of sleeping together to any group of loving couples, and one begins to wonder if a mutual sleep strategy shouldn’t be part of a prenuptial contract. Studies back up that impression.

In his book “Sleep,” Harvard researcher J. Allen Hobson reports that neither person sleeps well until both do.

Research also shows that even compatible couples routinely disrupt each other’s sleep, say experts for the Better Sleep Council, an industry group whose goals include helping discordant couples resolve their differences with products.

Another study shows that couples who sleep together dream more than people who sleep alone, spending more time in a state called rapid-eye-movement, or REM, sleep. That means couples spend less time in the more refreshing deep sleep.

It apparently takes at least 10 minutes of undisturbed sleep before deep sleep can begin. If one partner disturbs the other during those 10 minutes, the clock apparently is set back to zero, says Dr. Peter Hauri, a sleep expert at the Mayo Clinic, in his book “No More Sleepless Nights.”

This can be troublesome because everyone changes positions 40 to 60 times during the night, including a dozen full body turns. And, studies show, each time one partner moves, the other moves within 20 seconds.

Despite bedtime blues, Julie Griffith’s marriage has held up nicely for nine years.

“We are the classic, diametrically opposed couple,” says the Santa Fe Springs woman.

The problems started with the couple’s first bed, a standard-sized double that, industry experts are quick to point out, gives each person as much width as a baby’s crib.

“We were always beating each other up--inadvertently,” Griffith says. “Even after we went to a queen-sized mattress, we share it with three cats. You’re kind of stapled in place by the weight of these cats.”

Movement is a real problem, she says.

“When he turns himself over, he must raise himself up and hurl himself back down. I just hang onto the side and try to ride it out.”

Of course, she’s not perfect.

“My feet are so cold, I have to wear socks to bed year ‘round. If my feet touch him, he’ll gasp and sit straight up.”

Griffith says each of them has lost sleep because of the other. And each has been known to sneak into another room to get some rest.

“I think it’s part of (marriage),” she says of their sleep disturbances. “I wish there was some solution.”

Experts say many of the problems couples experience are territorial. Most can be solved with etiquette, compromise, sensitivity--or professional counseling.

Boston doctor Richardson recalls one patient who was worried about incompatibility in his pending marriage. He was a night owl who loved to stay up late. She was a lark--early to bed, early to rise.

“The owl said, ‘I can’t get out of bed until noon, and my fiancee said I have to fix that or she won’t marry,’ ” says Richardson. The doctor says he taught the man techniques to gradually change his body clock “to make the owl into a lark. With a motivated person, it’s possible to bring people into synchronicity.”

Other sacrifices might also be necessary.

The person who simply has to sleep on the left side of the bed should be allowed to have that side. Earplugs and eyeshades can solve the problems of too much noise and too much light. Experts say optimal sleep occurs when room temperature is in the mid-60s. If that’s too cold for one partner, he or she can add a blanket or a layer of pajamas. Individual choices, like pillows and clothing, should be respected.

As for the age-old problem of whether the mattress is too soft or too hard, the bedding industry has sunk millions into trying to find the perfect mattress for the incompatible couple. Several models are now available that respond exactly to the size and weight of the person sleeping on them.

Still, there are problems--those related to lifestyle and even personality--that can’t be solved by technology.

Some couples resolve conflicting styles with sensitivity and manners.

Susan, a Los Angeles businesswoman, and her husband have solved most bedtime problems during their 15 years together.

“I think one of the accommodations we made is I go to bed at least an hour before Donald,” she says, adding that she reads for about 20 minutes before falling asleep.

“If he comes in and I’m just beginning to drift off and he wakes me up, I have trouble falling asleep again. When he begins to fall asleep, he’s a bundle of jumping around. But if I’m already asleep, it doesn’t bother me as much.”

Susan says they are not picky about who gets what side of the bed or what temperature the room is. She says she can’t imagine not sleeping with her spouse: “If we are separated at night, I’m not comfortable at all. If he’s out, I feel less secure.”

But there is that one little, uh, quirk .

“I can’t sleep facing him,” says Susan. “He said, ‘Why don’t you sleep facing in?’ But I can’t. I don’t know what that means. Maybe we’re not happily married!”