"The position of your knees while sleeping affects the position of your hip, pelvis and spine. Putting a pillow between your knees can help to bridge that space and allow your hips to stay stacked," she said. "Keeping your hips stacked helps to not rotate your spine, which can become uncomfortable after sleeping in a rotated position for a while."

Like the name suggests, a knee pillow is designed to be placed between your knees when you sleep on your side and eliminate pressure on your hips and lower back. Terranova added that over time, it's possible to develop stiffness, aches and pains if you are sleeping with your spine in a rotated position, and that her clients notice a big improvement when using a knee pillow. But she also suggested using a larger body pillow to add provide for your upper body.