Dizziness when you turn or stand up can often be related to inadequate hydration, but anxiety can also cause the symptoms you describe. Though these symptoms are common and unlikely to be serious, you should schedule an appointment with an internist who can exclude more dangerous causes of dizziness and a fast heart rate, including an abnormal heart rhythm. He or she can look for signs of a heart problem on exam, and possibly do a simple test called an EKG that assesses your heart’s rhythm. In the meantime, drink plenty of fluids (at least 32oz. daily) and try to note in detail the circumstances under which you have had these symptoms. If you have another episode of dizziness with a fast heart beat, you should go to the emergency room where they can check your heart rhythm at the time you’re having these symptoms.