What is POTS? Postural Orthostatic Tachycardia Syndrome, explained.

Christina Applegate's daughter Sadie recently revealed she was diagnosed with Postural Orthostatic Tachycardia Syndrome, or POTS, prompting questions about the condition. 

POTS causes your heart to beat faster than normal when you go from sitting or lying down to standing up, according to the Cleveland Clinic. 

"Your body's autonomic nervous system balances your heart rate and blood pressure to keep your blood flowing at a healthy pace, no matter what position your body is in. If you have POTS, your body can't coordinate the balancing act of blood vessel constriction (squeezing) and heart rate response," the clinic's website explains. "This means that your body can't keep your blood pressure steady and stable."