Is It Normal To Experience Dizziness After Taking Depo-provera?

My girlfriend is 5'6 130 pounds and had her first depo provera shot two weeks ago. About a week after it she almost fainted from being dizzy. They took her to hospital and said is was dehydration. She has been drinking fluids and eatinf salt like they told her. She is still getting dizzy and now having occasional chest pains. She said today her stomach hurt. They did pregnancy test at hospital and it came out negative. Any idea on whether this is side effects or if she is pregnant???