I have a similar problem, after a lot of back and forth (I didn't have obvious triggers and I had a few red herrings) and two tilt tables, both of which came back positive, but with very different reactions, I was diagnosed with vasovagal syncope. It took over my life. The funny thing is that I had periods of this in high school, but I hadn't had a problem in a long time, my last severe bout was 5 years ago, with just twice yearly episodes in the meantime (an amount I can live with). In addition, I have hypoglycemia, so Dr.'s and family chalked it up to that for so long, until I started measuring sugars concurrent with episodes and was able to document that my sugars weren't low when I was having these.
Unfortunately, the midodrine didn't do anything for me (I still passed out several times a day), neither did the florinef. I'm now on pindolol (a beta blocker) in addition to these other medications and doing daily tilt training, and I'm out of work for a few weeks. I seem to be doing better, but its tough to tell because everytime I get dizzy, I lay down and put my feet up for as long as it takes, I won't have that luxury when I get back to work. I still have daily dizzy episodes and I faint about 1-2 a week even with the adjustments I've made, I just hope that won't translate into even more faints when I get back to work.
I wish you the best of luck!