I am 41 years old, and a woman, in general good health. For the last 12 hours, I am not able to stand up for more than two or three minutes (and sometimes not more than a few seconds) before I begin the process leading up to passing out (things going black, experiencing sounds as though they are far away, etc.) Along with this pre-syncope, my legs go week and my breath becomes labored. So far, I've been able to lie down before actually fainting, but the labored breathing takes as long as 15 minutes of lying absolutely still (no exertion) to subside.

As for the breathing issue, I'm not sure "labored" is the right term. So I will describe: I am able to breathe, but my breaths are rapid and very deep, almost gasping. I can't control this as it's happening - it's some kind of automatic response to what seems like my body not being able to get enough oxygen. The last time I got up, after three steps, my breath was as described and there was pain in my chest. It resolved after about 20 minutes of lying down.

Again, if I do not exert myself long enough to recover, I able to sit up in bed and breathe normally without triggering the pre-syncope. It's once I stand up that it all goes to shit. :) When resting, as now, I feel weak, but otherwise have no other symptoms. I took a few glucose pills to rule out low blood sugar. Nothing changed.

These are somewhat scary symptoms, but given what's happening, I can't drive to an ER and I don't want the drama of calling an ambulance if this is nothing serious. And again, as long as I am at rest, I'm pretty much okay.

What are the possibilities of what could be causing this?