Answers, built from engineering.

A mattress feels uneven when one area has lost support while the rest hasn't—usually a softer, lower center against firmer edges. Sometimes the unevenness is the foundation underneath, not the mattress itself.

Yes—a mattress can cause hip pain two ways: too little support, so the hips sink and the joint is strained out of line, or too little cushioning, so pressure builds against a hard surface. A sagged center is a common culprit.

First-night support and long-term support are different things. A new mattress feels supportive before any material has fatigued; over time the center loses springback and the support fades, even though the showroom feel was real.

Body impressions form where you lie most. Some shallow settling is normal, but a deepening impression in the center is usually the support beneath failing—since body weight concentrates there and fatigues it first.

Pain worst on waking that eases through the day is the clearest sign the cause is your sleep surface. The center sags, your spine bends out of neutral overnight, and it recovers once you're upright and moving.

Common, yes—normal in the sense of unavoidable, no. Most mattresses are built the same edge to edge, so the center fails first on a predictable timeline. But it's a result of construction, not a law of nature.

A dip forms in the middle because that's where your body puts the most load. The center third loses support first, and by the time you see the dip, the structure underneath has been failing for a while.

More weight means more force on the same center coils every night, so they reach fatigue sooner. Early sag for heavier sleepers is a construction mismatch, not misuse—the center wasn't built for the load.

The middle feels softer because the support underneath has started to give way. The center third fatigues first, so the surface above it sinks more easily. A softer middle is usually lost support, not added comfort.

Sagging within a year usually points to a weak, unreinforced center that fatigued early, or a failing foundation under the mattress. Check the base first—a broken slat or box spring mimics mattress sag and is the cheaper fix.

Waking with lower back pain has several causes, but if it's worst on waking and eases as you move, the sleep surface is a prime suspect. A sagged center lets the hips sink and bends the spine out of neutral all night.

The middle feels softer because that's where you sleep—and where support has worked hardest. The center third fatigues years before the edges you rarely lie on, which still feel firm because nothing has worn them down.