Several months ago, Mark Keam started to notice a sharp pain in his neck that radiated down his left arm and was accompanied by an "electric shock" sensation and constant tingling.

"While I was sleeping, every time I would turn one way, I would feel that really sharp pain even more," said Keam, 55, a Democrat in the Virginia House of Delegates. Once, he said, the pain in his arm was so intense that he cried out in the middle of the night, alarming his wife.

Keam, who has since been diagnosed with a condition that causes compressed nerves in the neck, said his symptoms were probably exacerbated by his sleep position of choice: For as long as he can remember, he's fallen asleep on his stomach — "a little like a frog" — with his head turned to one side.

Following advice from his doctor, Keam said, he is attempting to join the legions of back and side sleepers, though fighting the "automatic impulse" to flip on his stomach hasn't been easy. "The pain is definitely better," he said. "I haven't woken up because of pain so much as woken up because I feel like I've been in the same position for a little too long and my body's starting to get uncomfortable."

While the position in which you fall asleep is just one piece of the sleep-hygiene puzzle, experts said it can be key. As in Keam's case, the wrong sleep position could exacerbate an underlying medical condition, while the right one might alleviate symptoms and increase comfort.

Here are the pros and cons of different sleep positions, and how to pick the best one for you. We also have advice from experts about appropriate pillows for back, side and stomach sleepers, and tips for learning how to stay in a new position.

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On your back

For generally healthy people, sleeping on your back, or in the supine position, may help with spine alignment, the experts said. It can also help prevent or ease back and neck pain, because it provides more support.

It's important, though, to make sure you have a quality mattress and an appropriate pillow, said Timothy Morgenthaler, co-director of the Center for Sleep Medicine at the Mayo Clinic. Many people who sleep on their backs may develop neck pain because they're using a pillow that's too thick, he said.

"If you are on your back and you have a 10-centimeter-thick pillow, it tends to kind of flex your neck forward, and that may put undue stress on parts of the cervical spine and discs and muscles," he said. "If you're somebody who really likes to sleep on your back, then you may want to experiment with a narrower pillow rather than one of the big, super fluffy ones."

Rachel Salas, a sleep neurologist at the Johns Hopkins Center for Sleep and Wellness, also recommended using a second pillow or a rolled towel under the knees to prop them up, which can relieve some pressure on the lower back.

But the supine position is not for everyone, such as people who have obstructive sleep apnea or snore. "Sleeping on your back can obviously make snoring and apnea worse, just because of the way gravity works against you when you're on your back," Salas said.

Snoring, which is often associated with sleep apnea, usually happens when a person's airway is obstructed, said Rafael Pelayo, a clinical professor in the sleep medicine division at Stanford University's School of Medicine. "The biggest thing about snoring is the tongue, and so the tongue will slide back when you sleep on your back."

While positional therapy, which uses various techniques to help people stop sleeping on their backs, is a treatment option for milder sleep apnea, Pelayo said, it may not be sufficient in moderate or severe cases.

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On your side

"For the most part, sleeping on the side seems to be the most natural way of sleeping for a lot of people," Pelayo said.

Side sleeping is often the recommended position for people who can't sleep on their backs because of an underlying health condition or pregnancy, experts said. And depending which side you sleep on, it could help lessen symptoms of pain, heartburn and reflux, as well as potentially increase comfort for people with heart failure.

If you have shoulder or hip pain, avoid sleeping on the side that's bothering you, experts said. For chronic back or neck pain, Pelayo said, sleeping on the side might be beneficial because it can take the pressure off painful areas.

Sleeping on your left side and with your upper body slightly elevated is the ideal position for people with heartburn or reflux, Salas said. "It all kind of centers around where your organs are."

In this position, the majority of the stomach is below the esophagus, said Raj Dasgupta, a pulmonary and sleep specialist and spokesperson for the American Academy of Sleep Medicine. "You want gravity to be your friend in most cases," he said.

Sleeping on the left side may also be better for pregnant individuals, Dasgupta said, because it can take pressure off the critical blood vessel that supplies the heart.

Sleeping on the right side, however, could be more comfortable for people with enlarged hearts, according to a 2003 study published in the Journal of the American College of Cardiology.

Morgenthaler said pillow loft (its height/thickness) is an important factor in ensuring comfortable side sleeping. If you're sleeping on your side without a pillow or using one that's too thin, that could cause the head and neck to be flexed on one side and extended on the other, he said. "You want a pillow that's sufficiently thick so that your neck is in a more neutral-type position, and it turns out that, on average, that's about 7 to 10-ish centimeters."

A pillow between the knees could also help with discomfort or osteoarthritis, Dasgupta said, which may be exacerbated by sleeping with your legs folded together.

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On your front

People who snore or have sleep apnea may have an easier time if they sleep on their stomachs because it can help keep the airway more open, Morgenthaler wrote in an email. But the downside of the prone position is that it tends to "create a lot of pressure on various muscles and joints," he said, because people who sleep on their fronts typically have their heads turned to one side and their arms in unusual positions or pinned underneath their torso.

Dasgupta agreed: "You can imagine your neck is on the side, gravity's pushing down on your spine, so I'm really not a big fan of sleeping on your stomach."

Given the potential increased strain on the body in this position, Morgenthaler said, stomach sleepers may want to avoid using "very thick" pillows so they don't put added stress on the cervical spine, shoulders or lower back.

Still, experts emphasized that sleep positions are individual and you should go with that works for you. "What you want is comfort, and that comfort will help you sleep deeper," Pelayo said.

If, however, you're realizing that your sleep position is not ideal, keep in mind that it may take some time to get used to a different way of sleeping. And, Pelayo noted, it's important to remember that you naturally move in your sleep. "Even if you wake up in the same position when you first started, it does not mean that you don't have a journey throughout the night changing positions," he said.

Strategically placed pillows and devices intended to help you stay in a certain position may be helpful, experts said. There are belts and vests designed to make sleeping on your back uncomfortable and wearable technology that can sense if you're on your back and emit vibrations prompting you to turn on your side.