A mattress may develop a noticeable dip in the middle if it’s a bed shared by two side sleepers, if it has gotten old, or if the users allow their child or dog to sleep in the middle. Side sleepers tend to sleep as close to the edge of the bed as possible, and over time this can lead to noticeable sagging in the center of the bed. Side sleepers that tend to adopt the spooning position when falling asleep may also unintentionally be creating a mid-sag, as the body of one of the ‘spooners’ is typically positioned directly in the middle of the mattress. Children and pets can also contribute to a mattress sagging in the middle, especially if they are consistently allowed to sleep in the center of the bed.