I have a 2002 with the big living room slide. When I look underneath when the slide is open there are iron bars that have an adjustment bolt and locknut on the outermost end of the rods. The bolts press up against angle iron brackets. If your is like mine my guesses would be either the bolt is loose or fell out, or the angle iron has rusted through letting that side drop. Failing that I'd check the inboard end of the slide rod.
Let us know what you find.
2002 Four Winds Infinity 37', 2 slides, F53 with V10, 22,500# chassis, CHF. 4 of us and a German sheperd.