I try to look up the ceiling whenever I stop rolling from our extended rolling drills. This helps me dissipate the dizzy feeling. Also taking a few deep breaths immediately after will help. And please don't stand up immediately if you feel dizzy because you might fall over and injure yourself. Wait awhile, I'm sure your instructors will understand for safety reasons.
As advised in the previous posts, practice will help you in reducing the dizzy feeling after rolling.
Hope this helps and keep on training! =)