Explaining how you injured yourself can be demoralizing, and if you hurt yourself in bed, it can embarrassing, especially if you were just sleeping.
Waking up with a crick in your neck means waking up on the wrong side of the bed, and one way to avoid this "sleeping injury" is to avoid sleeping on your belly. Tucking yourself into bed on your tummy might feel safe and sweet, but since you have to turn your head just to breathe, you're disrupting the alignment of your neck. This position not only leads to a stiff neck, but it can be rough on your lower back too. Breathing deeply is essential to quality sleep, and when you sleep on your belly, you compress your lungs.