String theory has discovered a new symmetry between large and small.
According to Geoffrey West, a scientist at a physicist at Los Alamos National Laboratory, "Everything around us is scale dependent, it's woven into the fabric of the universe."
One of the most fundamental physical principles is conservation of mass, amended by Einstein to conservation of mass / energy. To shrink, it's not enough that the object's atoms get closer together, because it's mass and weight would be the same; what fun would it be being 6" tall if your weight were still 180 pounds?
Advanced physics holds on some (very) slim hope, though. Maybe the extra mass could be shunted aside into one of those extra dimensions of string theory.
So let's say it happened.
Six inches is one twelveth the height of a six foot tall person. Surface area varies with the square of the linear dimension, while volume varies with the cube. That means volume would shrink much faster than height. You'd be 1/1728th your former volume and weight, but have 1/144th the surface area. In other words, you'd have twelve times the surface area through which to lose heat. You'd have to metabolize (eat) that much more (relative to weight) and time would seem faster.