Hi and welcome!
Those are questions you should ask your physician. If you want, you can ask one of our experts at http://birthmark.org/experts.php
I usually hate it when I miss a day of working out and I'm a big slug. I run for 30 minutes and do a bit of yoga and when I don't get to do it in the morning, I don't feel so good the rest of the day.
I can't see anything wrong with a brisk walk, but, as I said, I would make sure before I did anything much more than that.