Originally a drug for hypertension and now is used "off label" for PTSD symptoms including; nightmares, reexperincing, avoidance, numbing and hyperarousal. I couldn't have found one more perfect. I will have to see how well I tolerate the side effects, but the study that I read says the drug is well tolerated.
My doctor prescribed 1 mg titrated up to 2 mg over two weeks. I took my first dose tonight, so far the only side effect that I can discern is a massive headache, but to me I have those all the time. Acetaminophen took the headache away, so no problem. I will have to watch out for those over time.
Update: 1/15/2013 - I am still taking Prazosin, I am up to the maximum dosage for nightmares at 5mg. It still works today, still deal with the possibility of fainting but not as bad as when I first started taking it.