POTS is a form of dysautonomia that most often shows up in teenagers but can affect anyone at any age. It occurs when there is a 30 point jump in heart rate when someone goes from sitting to standing. This is just the diagnostic criteria, though, and POTS involves a lot more than just your heart rate...
Dysautonomia (sometimes called autonomic dysfunction) is an umbrella term for a group of conditions that deal with your autonomic system
--aka everything that happens automatically in your body. POTS falls under that umbrella, and that means everything your body is supposed to do all on its own either happens improperly or doesn't happen at all. As you can probably imagine, this can cause a lot of problems.
POTS can (and, in some cases, does) effect every part of your body, from your brain all the way down to your toes. Many patients experience dizziness, fatigue, heart palpitations, blood pooling in their extremities, poor temperature regulation, and many...many...more... Sheesh, just writing this list is exhausting... You can check out my POTS Problems comics for a more comprehensive list of common symptoms.