Sharing a bed is sometimes one of the challenges of a relationship, even for couples deeply in love. Lisa, 33, in Wiesbaden says physical contact with her boyfriend is something she can do without when she wants to go to sleep. Her boyfriend Martin used to be a cuddler but he isn't bothered by Lisa's desire not to.
"It was different with my previous girlfriend," Martin said. "But the way it is now is completely OK with me."
Both are fully satisfied with their relationship and with their sex life.
The researchers have given names to different sleep positions and interpreted their meaning.
Couples who sleep back to back with their bottoms touching, for example, are bonded sexually and sensuously but might like independence.
What is commonly known as the spoon position, in which couples snuggle up to each other front to back, betrays a dominance of one partner over the other.
Couples freshly in love often sleep intertwined in a love knot, the researchers said.
A couple who don't touch at all over night and who turn their backs toward each other indicates tension, Goulston and Dunkell said.
But perhaps it is just a matter of comfort, as is the case with Lisa and Martin. They are, however, more of an exception because one partner's need to snuggle and another one's habit of pulling the covers off are things that sometimes lead to arguments.
Sleep specialists and relationship counsellors, however, warn not to read too much into the interpretations.
"Sleep habits are very individual and therefore shouldn't be overestimated," said Hamburg therapist Elmar Basse.
More than anything else they have to do with what a person is used to, and it is known that they can change, sometimes easily and sometimes with difficulty.
"My boyfriend was almost appalled when we spent our first night together and I wanted to share my comforter with him," said 29-year-old Katja from Hamburg. But despite his reaction, she didn't get the guest comforter out.
"Today we almost always sleep under one cover."
Stefan and Maja in Duesseldorf have been sharing one cover for 12 years. Nothing else would suit them. "It's so cozy," they said glowingly.
Their agreement on the matter, however, is unique among couples.
"Most marriages should fail based on the fact that individual partners have different biorhythms," said Heinrich Becker, leader of the sleep laboratory at Marburg's university clinic.
Christoph Schraivogel, who runs the Internet portal www.schlafkampagne.de, is convinced that it is wishful thinking that two people can sleep restfully under one cover.
And there are good reasons for that.
"For many people, closeness during sleep is simply uncomfortable and it affects peaceful sleep," said Werner Cassel, a psychologist at the Marburg sleep laboratory.
Many people are extremely restless at night and suffer from restless leg syndrome, which causes pain and constant twitching in the legs. Their muscles also become sore.
Basse said it could be very bad for relationships.
"People who don't sleep well overnight and feel knocked out when they wake up possibly will direct their irritability toward their partner," he explained.
That's why sleep experts highly recommend a sleep routine.
"Particularly when the sleep habits are very different, partners can reach an understanding that they go to bed together, cuddle for a while and then slide over to their respective side of the bed and under their own cover," Cassel advises, adding that separate bedrooms are not disastrous to a relationship.
"There are very happy couples who sleep separately."
Basse also knows of couples who have been together for years sleeping in separate rooms.
"When a relationship is based more and more over time on trust and harmony, the sexual aspects often decline, which is perfectly fine for many couples," Basse said.
What is problematic is when both or neither partner wants any physical contact. "Then there is something wrong," he said, especially previously enjoyed close contact while sleeping.
Those who want to sleep closely with their partner should make it clear at the beginning of the relationship. Sometimes people, who convert to sleeping alone, sometimes revert to being cuddlers in certain phases of a romantic relationship.
"Couples newly in love usually seek closeness," Basse said. So at the beginning of a relationship, snuggling that at first feels strange can become the norm.
It's also important for couples who have been together for a long time to talk about their needs and seek solutions.
Neither partner should feel insulted if his or her partner rolls over in the middle of the night, but it's equally wrong to ignore criticism.