You are a normal person living in the modern day. You are alone in your home minding your business when all of a sudden a portal opens up underneath you. Before you can react you fall in! As you travel in the portal you both travel back in time and your body compresses into itself causing you to shrink.

Eventually the portal spits you out in an unknown time, in an unknown place, in an unknown size.

(What year are you in now and what size did you shrink to?)