POTS is very common and is mainly associated with rare conditions. Although POTS is not that rare, it is unrecognized or insufficiently known by doctors. POTS (= Postural Orthostatic Tachycardia Syndrome) has been briefly described as a defect in the autonomic nervous system. This means that all functions in the body that you have no control over are disrupted, with the main complaint of the  significant increase in heart rate when standing / walking.
The term dysautonomia is an umbrella term for many autonomic dysfunctions, so not only POTS but also OH (= orthostatic hypotension) and OI (= orthostatic intolerance).
POTS has several subdivisions and can come in a few different types: Hyperadrenergic POTS, Hypovolemic POTS and Secondary POTS.

Gastroparesis is also called as delayed gastric emptying or gastric paralysis.
This condition is characterized by the fact that the stomach muscle does not contract enough to digest food - the food stays in the stomach longer than normal, which can cause various symptoms.

The cause of this condition is still unknown and is sometimes difficult to diagnose - why this condition suddenly occurs can be related to a variety of factors including POTS.