The warm light surrounds you and fills you with pleasure beyond your imagination. Your brain shuts off completely as you go through your first big change. Your clothing disappears, as you grow in height to be about five and a half feet tall. Your breasts go from non-existent to b-cups and hair grows around your crotch/pits. The six year old you once were is now a fully grown woman in a near instant. However, this is only the start of something even bigger.
As you stand there, naked and drooling from lack of brain activity, your height begins to slowly decrease. The beautiful human face you once had is starting to look more and more ape like. You begin to quietly ook, as vocal cords quickly degrade to the point where you can no longer speak. Hair begins to grow all over your until it starts to form a thin fur coat. You begin to slouch, as standing upright is getting harder by the second. As you breast shrink and sag, your feet become hand like. Now under four feet high, you devolve to the point in which standing upright is nearly impossible. As some drool hits the floor, so do your knuckles.
Your quite ooks start to become more high pitched. As tail starts grow, as you begin to shrink faster. Your hands and prehensile feet now look and a lot more like paws. As you reach the size of a small house cat, a snout starts to grow out of your lemur-like face. Now looking more like a squirrel than an monkey, you loose all the hair on your tail and your four legs shorten. You reach both the size and look of a very small rodent when you eventually stop shrinking. Then, you slowly start to grow. Your tail thickens, as your fur coat starts to become thin. Scales start to quickly replace fur, as your reproductive organs reassemble for producing eggs rather than live births. The remnants of your breasts and ears disappear completely. As you reach the size of a medium sized dog, all of your fur is replaced with scales. You become cold blooded, and now look like a very large lizard.
Just then, your body begins to shrink again. Your scales become very slimy, and your feet start to become webbed. Breathing starts to get harder. As you return to the size of a small rodent, a lot of the articulation in your legs is lost. Your neck is completely absorbed into your body and gills appear in its place. The four legs you once had have now morphed into four fin-like appendages. These quickly turn into proper fins, as two more fins grow on your back and tail. Flopping over on your side, breathing on land becomes impossible. Only the light is keeping you from dying. Reaching the size a small fish, your getting thinner as well. All your fins, with the exception of the one on your tale, are absorbed into your body. Your body continues to simplify, giving you the appearance of a worm. Every single feature on your body disappears, leaving you a blob of tissues.
Finally, you begin your last leg down the evolutionary ladder. The cells begin to rapidly decrease. From the millions, to the thousands, and finally to a single cell. You quickly loose complexity, going from a eukaryote cell to a prokaryote like organism. Now only a blob of DNA with a membrane, you begin to break down. The light goes off, your membrane dissipates, leaving a large puddle of hot thick ooze in your place.