Wondering if you know what caused the POTS? POTS is usually caused by chemical insults like antibiotics and other phramaceuticals, hidden infections or trauma. Also it might be a good idea to monitor his heart rate. I can imagine how difficult it must be for a teenager to deal with POTS. It can happen that when he starts to become anxious it means his heart is racing and it is time for him to lie down until he feels more comfortable. Increase water intake, excerise as much as he can lying down and as much as possible very pure diet. With the portable blood pressure cuff it is very easy to monitor his heart rate so he can know when he needs to lie down and prevent a huge stress response. Maybe you are already doing these things. Also CBD works wonders for some folks on the spectrum. It must be organic and grown in the USA. A meditation like TM would help normalize his autonomic NS. Just a sharing here as I am not an MD, but a POTS surivor on the spectrum and HA HA I am not a teenager; I am 73. Hope this sharing helps a little.