I have a two story house and some of the joists between the floors are sagging about an inch or two. When I walk around upstairs I can feel the level difference and downstairs you can slightly see the lines of one or two joists in the ceiling. These joists happen to be the ones our bed is on so I'm guessing that is the cause. There aren't any cracks or gaps anywhere. I'm not sure how concerned I should be, and if it's normal or needs to be fixed.
oh, the house is around 30 years old.