When you settle into bed at night, you might instinctively sleep with one arm under the pillow. For some people, this position feels natural, comforting, and helps them drift off to sleep quickly. But ...

Placing your arm under the pillow is a very common gesture. It’s part of the so-called “fetal position,” named because it mimics the way a fetus curls inside the womb. People who choose to sleep this ...