The first thing you know is that you are shrinking. Actually, it's the only thing you know. So yes, you are getting smaller. That's for sure. You feel yourself getting smaller and smaller. Compressed, in fact. It's not painful, but you can feel it. However, it also sparks up great fear in your mind and after all, with good reason. Getting smaller implies you are bound to be more vulnerable, and few pleasant creatures are tiny. Besides, you know full well that you've done something awful so the chances are you're in for an awful ride. The question, is, as what? What will your life be as of now? What people will you meet? What will you do? As what, or who? You can only quake in fearful anticipation. It could be anything but chances are it will be horrid. You've been sentenced as a punishment after all. And now that you finally face the consequences for good, you reflect on the ignominy of your actions. Indeed how all the people you've wronged in life might have felt as you tricked them or were plain mean to them. Suddenly your fun as a bully sounds like a waste of time that could only bring you to this sentence. You will suffer and no one will cry for you. And why should they? You've behaved like a horrible selfish jerk through and through. People were happy to see you go and to be rid of you. So you're on your own. And you don't even know if even your memories will remain intact or if you'll start behaving differently. The possibilities that await you are endless and frankly, terrifying.
Then you finally become aware of your new surroundings.