If you have ever felt a sudden wave of dizziness after abruptly standing up, you are not alone. Lightheadedness upon standing up can be caused by a low heart rate. When you stand up quickly, the blood in your brain travels towards your feet due to gravity, and it may not return to the brain for a few heartbeats if you have a slow pulse. This causes the brain to undergo a transient lack of oxygen, causing you to feel dizzy for a few seconds. If this happens to you occasionally, there is no need to worry, but if it happens constantly and is really severe you should see a doctor to make sure it isn't caused by an underlying condition.
Be sure to see your doctor immediately if you dizziness co-occurs with chest pain, loss of speech or a change in vision.