I slept on the same pillow for five years — a $12 polyester lump from a big-box store that had flattened into something resembling a pancake with lumps. My neck hurt every morning. I blamed my mattress, my desk chair, my “bad posture.” Then I stayed at a hotel with good pillows and woke up without pain for the first time in months.

The pillow was not magical. It was just the right height for my sleep position. That is the whole game: your pillow’s job is to keep your spine straight from your neck to your tailbone. The height you need depends entirely on how you sleep.

Side Sleeper: High and Firm

Side sleeping creates the biggest gap between your head and the mattress — your shoulder pushes your head up. You need a loft of 4-6 inches and firm support so your head does not sink through the fill. Memory foam or a dense latex pillow works. Some side sleepers do best with a contoured pillow that has a higher side for the neck and a lower center for the head.

Quick test: lie on your side and have someone look at your neck. If your head tilts down toward the mattress, the pillow is too low. If it tilts up toward the ceiling, too high.

Back Sleeper: Medium Height, Gentle Support

You need a loft of 3-5 inches — enough to fill the natural curve of your neck without pushing your head forward. Too high and your chin tilts toward your chest, straining the front of your neck. Too low and your head tips back, compressing the upper spine.

Memory foam with a contoured shape supports the neck’s curve well. Down and down-alternative pillows work if they have enough fill to hold their shape — a floppy pancake pillow does nothing for a back sleeper.

Stomach Sleeper: Thin and Soft (or No Pillow)

Stomach sleeping already twists your neck. A thick pillow makes it worse. Use a loft under 3 inches — a thin down pillow or a compressible foam pillow. Some stomach sleepers do best with no head pillow at all and a thin pillow under the pelvis to reduce spinal twist.

I replaced my pancake with a contoured memory foam pillow at the right height for side sleeping. The morning neck pain was gone within three days. Five years of discomfort, fixed for forty dollars.