The abortion itself is a straightforward local procedure that does not affect your body as a whole. What affects the body as a whole is general anesthesia. That is why they won't release you right away. You should be ok going into the office on Monday, but take it easy on the weekend. Just take it easy. If you are in Tokyo, you should be able to take public transportation back home on your own, but a ride from a friend would be nice, too. Japan has first rate health care. Plus, it is not an open heart surgery anyway. You have no reasons to worrry and your body will be just as healthy as before.