As a past stomach sleeper, this topic is dear to my heart. And spine. I recently injured my back pretty severely from standing up at work. I was just sitting at my desk and stood up to grab a dish and bring it to the kitchen. In the process of standing, an intense, sharp pain exploded in my lower back, immobilizing me. I set the dish down and grabbed my back like those commercials of elders with back troubles. When the pain didn't subside, I slowly eased back into my chair. The pain continued for over an hour before I could even turn left or right in my chair. Another hour later and I could walk again. It still hurt like hell though, so I emailed my naturopath to see if I could visit their in-house chiropractor. Two hours later I was in the middle of my first-ever chiropractic appointment. After some popping and locking, we got to talking about sleep positions. Turns out sleeping on your stomach with your neck turned 90 degrees to the left or right isn't the best for your spinal alignment. So let's look at our options.
Stomach Sleeping - Bad
While this position does help with snoring and sleep apnea, it doesn't do much else good for you. The weight of your body flattens the curve of your spine which can lead to back pain. Having your neck turned hard to the left or right also puts unnecessary strain on the neck. This is the worst position to sleep in, which unfortunately is what I've grown used to over my 26 years of sleeping.
Side Sleeping - Good
Side sleeping is the most popular position to sleep in. Because of the position of your heart and all your other organ goodies, sleeping on your left side can reduce heartburn and acid reflux! For the ladies with a bun in the oven, sleeping on the left side can also improve circulation to the heart, which I hear is a good thing. Side sleeping isn't all rainbows and butterflies, though. Unless you consider a numb arm 'butterflies.' While on your side, your body weight on your lower arm may compress your muscles and nerves. Your shoulder also takes a lot of the weight, constricting the neck and shoulder muscles. While this position isn't perfect, it's much better than stomach sleeping.
Back Sleeping - Transcendent
Sleeping on your back is the most natural and neutral position possible! It's definitely not the most comfortable, but it could save your spine in the long run. The best-case scenario is to lay on your back with no pillows and your arms to your sides with palms up. Yogis know this pose as shavasana (Wikipedia). In addition to the spinal benefits, your face will also be better off. Your skin will be exposed to fresh air and not squashed against the pillow, leading to fewer wrinkles. One thing to note, however, is that back sleeping encourages snoring and sleep apnea, so if you have issues there, roll onto your side for a better sleep.
"But I can't sleep on my back!"
We've put a man on the moon. You can sleep on your back. Before my back injury, I tried sleeping on my back occasionally, but could never fall asleep. There was something about the position that kept me awake. I think half of it was the psychological feeling of having your face exposed to a large open space. When your head is smashed in the pillow, there's a feeling of embrace with no room for thought. But when you're facing the ceiling, all that empty space encourages nighttime ponderings. The other psychological hurdle is the vulnerability of your body. When facing up, you are more exposed to unknown threats. If you were sleeping on the ground or near the floor, someone could easily step on your front side, causing some serious pain. But these fears don't make sense outside of a camping trip or sleepover.
So in order to successfully sleep on your back, you need to adjust your way of thinking. When I lay on my back in bed, I think of myself releasing all the thoughts, emotions, and efforts of the day. It also helps to have just one not-too-thick pillow so your neck is as flat as possible. This position is also ideal for pre-sleep meditation. Having your palms up helps to open up your energy and get into a state of deep relaxation. When you can achieve this, you'll find yourself falling asleep comfortably on your back. It's a great feeling.