The Floor Is Sloping
Unless you drop a marble and it rolls to one side of the floor, or you spill a glass of water and the liquid runs to the same spot, you might easily miss a slight slope in your floor. When a formerly level floor develops a slant, it could be a sign that one or more of the joists that support the floor have rotted or broken, causing the floor to settle in that area.
A structural engineer should take a look at your home’s structural support system and determine a method for repairing it, which could involve replacing one or more of the floor’s structural members.