Note from the author, April 2023: Please visit the book's website, www.whatpotsreallyis.net, to see four changes I would now make to this book and how my thinking has changed since I published it in 2017. Postural Orthostatic Tachycardia Syndrome (POTS) is currently defined as a 'syndrome', a collection of symptoms for which the root cause has not yet been identified. This book aims to rectify this by arguing the case for POTS being considered a form of neurological injury to the limbic system following an antecedent trauma, such as a viral illness, pregnancy, surgery or psychological trauma (or a combination). Patrick Ussher himself had POTS but recovered by following a limbic system rehabilitation program (originally developed to treat Multiple Chemical Sensitivity) called the Dynamic Neural Retraining System (DNRS). After recovery, he set about mapping the idea of a limbic system impairment onto pre-existing research into POTS and found that it could explain many key findings including: NET protein deficiency (which is responsible for blood vessel constriction problems and resulting elevated heart rate upon standing), low aldosterone and poor sodium retention (which are responsible for low blood volume problems) and mast cell activation problems. This book will simultaneously act as a guide for those interested in using the DNRS as a treatment for POTS and also as a call for further research into the potential efficacy of the DNRS for treating POTS.