I was just speaking to someone that told me she got in the habit of sleeping with two pillows. I told her this isn't a great idea and that you should sleep with one pillow.
You see, typically when sleeping with 2 pillows on your back and your head is flexed forward; this flattens out the neck curve. Not enough pillow and it flattens the curve too. Not enough or too much on your side literally flexes the head toward the ceiling or down to the bed.
A neck pillow on the other hand helps you keep and improve that neck curve when on your back and for side sleeping; the pillow will keep the spine level.
Additional Reading Resources:
- What to do for 10 years worth Neck Pain?
- Neck pain associated with occipital neuralgia
- Will it hurt my neck if I use a firm level support pillow?
- Pillows that will help you stop slouching while you are sitting
- A Review of the Arc4life linear gravity pillow: What it offers