We bought our house last year and a friend of mine pointed out our sagging floors just in the main entrance area (First floor on top of the basement). There are around 5 rows of titles (each spanning 15 titles). The first row closest to the living room is perfectly straight while the second row has a slight downward slope all the way to the last row closest to the kitchen (less than 1/2 inch depth). It looks like it has stablized and it's not sagging any more. Both the living room and our kitchen area is perfectly leveled. Our house is around 18 years old and the tiles don't have any crack or loose grout (except in some parts as a result of poor tiling). What I want to know is that is this a bad tiling job? or sagging? Also if it has stablized do I need to worry about it? It's not noticable at all.
BTW, also there is height fluctuation between floor and the baseboards anywhere from 0-1/4 inches.