Your clothes start to feel baggy and big. This is because you are shrinking inside them! As you shrink, you clothes collapse on top of you and you are shrouded in darkness.
You can't see, but your sense of smell and hearing seems to be greatly enhanced. You also feel fur on your body and something snaking off from your spine (a tail?)
Seeing light up ahead, you scamper towards it and emerge from your trouser leg as a tiny mouse!