A few comments/bits of advice about LSD based on my own personal experience.
When embarking on your first trip, you must have a trip sitter; this is for your own safety. One thing you have to understand about LSD is that once you are really trippin’ hard (4th of 5th plateau) and you have completely lost any sense of self, you are completely incapable of controlling any situation you may find yourself in.
A personal anecdote might help make this a little clearer. When I tripped on acid for the first time it was one of the most amazing experiences of my life. I went and ran around campus while I was coming up. The shitty art in the quad took on a whole new dimension. I ran back to my apartment and shot a round of pool, a perfect round of pool, without my glasses or contacts, while everybody watched (so it has been confirmed, I didn't just trip that). BTW, I have never been very good at pool. After that I rolled around on the empty pool table, basking in the glory of total ego destruction, somebody put a bowl up to my mouth and told me to inhale. That helped make the whole experience a little more comfortable, but also made me hungry. So I pulled out my cell phone and called in the order, the pizza man was very confused. While I was on hold I tripped an entire conversation where I was telling the guy on the phone what a great time I was having, and he kept asking me for stuff like my address and phone number and name. Then suddenly I realized what I had done, or thought I had done. I hung up my phone and yelled at my friend "we have to get out of here, NOW, I told the pizza man I was tripping on acid and he said he was going to call the cops!" so we run to his car, meanwhile I am peaking. Peaking under stress is NOT fun. I had lost almost all sense of self but I was sure that when the owner of the body came back he was going to really screwed because he was going to be taking it up the ass in some prison. Everything turned out all right, but for about three hours I was laying on my friends couch FREAKING OUT, in a whole new way. I was sure that someone was coming to get me, the only problem was, I had no idea who the hell me was.
As for flashbacks, I really like my flashbacks; they have always been nice "extras" in consensus reality. Sometimes when I am sitting in my reading chair in my room, and somebody sparks up some reefer, and one of the right songs is playing, and the light levels are low, surfaces will start to brighten up and go Technicolor, and I see the people in the room in bas-relief. People have asked me "these can happen for the rest of your life now, aren't you worried?" to tell you the truth, no, not very worried, LSD flashbacks are like any other flashback, it is a naturally occurring anomaly in the unaltered human brain, a response to an event that elicits a lot of emotion, the only difference is my LSD flashbacks are a little more colorful. BTW, I have non-LSD flashbacks as well, those are the ones I worry about. The moral of the story HPPD is a much better alternative to PTSD.