It happens at least once a month like clockwork: I wake up after a solid eight hours of sleep only to realize I’ve pulled my back and can’t lift my arm past shoulder height.
It’s frustrating, because the pain shoots through my body like a knife, but even more so because I know it comes down to sleeping on my stomach — the only position I can actually fall asleep in.
My sleep posture is far from ideal. A large body of research shows that sleeping on your stomach puts pressure on the respiratory system, nerves, ribcage, and spine, while also increasing heart rate — none of which support quality sleep.
Sleep positions also affect health and mood in ways many people overlook, and experts say there is an optimal position to aim for: sleeping on your side.
This position helps keep the spine straight and aligned, since “it will help prevent stress points that may aggravate joints and connective tissue,” says Dr. Robert Hayden, Georgia-based chiropractor and American Chiropractic Association spokesperson.
Side sleeping is also important for people who snore or have sleep apnea, as it helps keep airways open, says Dr. Natalie Dautovich, assistant professor of counseling psychology at Virginia Commonwealth University and environmental scholar at the National Sleep Foundation. For pregnancy, side sleeping not only relieves pressure on the abdomen, but a 2012 study in BMC Pregnancy & Childbirth found that sleeping on the left side in particular may improve oxygen flow for both mother and fetus.
To maintain this position, Dr. Hayden suggests placing a body pillow under the torso to support the upper arm and knee. Dr. Dautovich also recommends a pillow between the knees to reduce pain and keep the pelvis aligned. The head should stay level with the mattress — not stacked on multiple pillows, which can strain the neck and spine.
While it may feel comfortable to prop your head up while reading or scrolling before bed, falling asleep this way isn’t ideal, says Dr. Kristina Petrocco-Napuli, Florida-based chiropractor and president of the ACA Council on Women’s Health.
When you’re asleep, muscle tone — which normally protects your joints when you’re awake — becomes lax. According to Dr. Hayden, if your head, which weighs around 13 to 15 pounds, isn’t level with the mattress while you’re sleeping on your side, stress points can form along the neck joints. Under normal conditions, muscles help keep those joints from shifting too far, but during sleep the brain doesn’t send the same protective signals. “Joints that are stressed will be eventually injured, and arthritic changes in the joint may manifest at some point,” Dr. Hayden explains.
So the obvious question is: if you’re asleep, how do you stay in one position? Beyond using a body pillow for support, mattress quality also matters, since a poor mattress can increase tossing and turning. A 2011 study in Ergonomics found that participants sleeping on sagging or overly soft mattresses reported poorer sleep quality. Dr. Hayden recommends a mattress firm enough to support body weight, with only slight give.
There is also a “wrong” way to side sleep. Sleeping tightly curled in the fetal position, Dr. Dautovich says, can restrict the diaphragm and make breathing less efficient. It can also place strain on joints and lead to morning soreness. “You can reduce the strain on joints by straightening your body as much as possible,” she says. She also advises avoiding resting weight on your arms during sleep, as this can cause numbness or a pins-and-needles sensation; instead, keeping the arms gently folded toward the chest may help.
If you’re not a habitual side sleeper, you may be more prone to waking up sore. But beyond short-term discomfort, poor sleep posture can also affect emotional, psychological, and cardiovascular health over time. “Certain hormones are designed to ebb and flow during the sleep cycle,” Dr. Hayden explains. “Growth hormones regulate the production of hormones that we use to repair tissues and heal, [which are] secreted during stage IV of the sleep cycle.”
If stage IV sleep — or REM sleep, which begins about 90 minutes after falling asleep — is disrupted, “you may find yourself gaining weight, getting sick and staying sick more often, and eventually having changes in your cardiovascular system such as hypertension,” he says.
And even if you spend eight hours in bed, constant tossing and turning can leave you feeling as though you barely slept. “Fatigue itself will make you not feel your best,” Dr. Hayden says. “The physical aspects of your health will spill into the emotional and mental aspects. When you feel your best physically, you’re more likely to have a positive self-image.”
Even if you position yourself correctly, you may still move around in your sleep, shifting out of your intended side-sleeping posture. Dr. Hayden says it’s important to look at stress levels and find ways to manage them before bed, since they can contribute to restlessness and disrupt sleep position.
“If you’re one of these [people who toss and turn], do something before you go to bed to offload your stress,” he says. While eliminating stress entirely isn’t realistic, small steps can help ease the body into a calmer state. Instead of scrolling on a screen that emits blue light and can disrupt circadian rhythms and suppress melatonin, Dr. Hayden recommends reading a book. “Let your mind go blank, or to a time or place that is relaxing and comfortable. Try a warm bath or shower to relax,” he says.
That said, you’re not doomed to a life of pinched nerves and sore muscles if you can’t sleep only on your side. At the end of the day, all the experts agree that comfort matters most. Other positions, like sleeping on your back, can also be beneficial if done correctly. For back sleeping, Petrocco-Napuli recommends placing a pillow under the head and another under the knees to support and level the spine. Adjusting pillow placement can also help support the natural curve of your spine.
It may sound like a lot to consider right before falling asleep, but with the right pillow, a supportive mattress, and proper alignment, better sleep is possible — and waking up without pain more likely. If discomfort continues, it’s best to consult a doctor to rule out any underlying issues.