I'm 30 and was recently told I have orthostatic intolerance.(Specifically, POTS and neurally mediated hypotension.) I am very uncomfortable upon standing or even sitting too long...feel weak and hollow in the chest and fatigued and anxious. I've also had other health problems such as dizziness and lower back pain while walking, over the past year. I have already researched many internet sites about this problem, but would rather have more personal point of views and first hand accounts of this illness. If anyone has any experience with tachycardia caused by upright posture, and feelings of pre-fainting spells, or has any first hand stories of this illness, I'd love to share. Thanks in advance. :)