If you have heartburnBest sleep position: Elevated head
Heartburn or acid reflux tends to be worse when you lie flat. So if you suffer from nighttime reflux, the most important thing is to keep your head elevated during your sleep. Back-sleeping is the healthiest sleeping position of all. "Slip a wedge-shaped pillow under your head (or under your mattress) to raise the head of the bed," says gastroenterologist Ken DeVault, M.D. The gravity will prevent stomach acids from backing up into the esophagus and causing heartburn. If you sleep on your side, lie on your left (not the right), so your stomach is lower than your esophagus.
If you have neck or back painBest sleep position: On your back
"Try to sleep on your back, with your back straight and head in line with your spine," says Dr. David Tuchinsky, author of Back Pain: It's All in Your Neck. This makes it easy for your head, neck and spine to maintain a neutral position. If you have lower-back pain, placing a pillow under your knees can alleviate some of the pressure there. Avoid sleeping on your stomach, as that puts the most stress on the lower back; it's also bad for your neck because in this position you have your head to one side for hours at a time.
If you snore or have sleep apneaBest sleep position: On your side or stomach
If you snore or have sleep apnea (a disorder that involves pauses in breathing while you sleep), sleeping on your side or stomach will help keep your airway open. Snoring is often worse when you sleep on your back because your tongue flops back against the back of your throat, causing everything to rattle more. It is important to speak to your doctor if you feel you have sleep apnea, because it can be severe and you may need other treatments.