Girlfriend is feeling dizy. Attention?

All day yesterday as well as this morning my 22 year old girlfriend has been experiencing dizziness when she bends over while standing and when she sits up in bed. She has not fainted or had any other symptoms. When she is standing or sitting or walking she feels normal. Exactly one week ago we had an issue where I did not wear a condom. However, the day after she took plan B as a precaution. After taking plan B she did not experience any of the possible side affects of it. I'm curious what her next step should be. Is it possible she is experiencing symptoms of pregnancy? Could she just now be going through the plan B side affects? Is there another more likely reason she could be feeling this way? If so should she seek medical attention?