I have had the exact same problem my whole life, beginning at age 12 and am now 55, and believe it or not, doctors have yet to find out why. It looks like you posted this a long while ago, but I am replying to it anyway. I know the feeling of fear of making commitments and follow through because one never knows when they are going to faint. It seems to follow a pattern. I had it in my early twenties, then it went away, and now it is back. I fainted on a city bus, about a month ago, in the middle of the night and cracked my skull. My diet is excellent, I work out, I do not smoke or drink and I take care of myself. I thinks stress tends to bring it on, and it is almost like stress after the event...I went through a horrendous divorce a year ago. During that time, did not faint once, but now making up for it. I tend towards low blood pressure anyways.
Keep dark shads on. Make sure you have a proper diet. Stop thinking so negative! or at least try. Ive fallen on my face a few time, and had awaken minutes later...your too worried..relax..don't try and complete projects on your own, let people help out..