I am 35, male, 60 pounds overweight (but I workout very hard regularly without problems). I have also had a stress echo and chest xray. I do have a history of PVC's. My oxygen levels, including my arterial blood gas test, was normal. My problem is that anytime I try to hold my breath at all, it feels like the "primal instinct" to breath takes over very powerfully almost instantly and I can't stop it...if I resist, I will get very lightheaded. I knew about this problem before, but I was having a CT scan to evaluate my hematuria and I couldn't hold my breath long enough. Can you tell me what this could be? It gets better and worse at differnt times, but again, I can always workout hard without an issue.