I almost wanna say it was always there but didn't notice until after I tripped... who knows by now all the shit I've done. I like the mini acid trips after sex, probablty has something also to do with endorphins. Flashbacks aren't something to really be scared of... vietnam vets have them in a whole other, way more terrible way that none of us here (don't think any vets frequent here) could ever imagine. I say just look at them as 'free trips' and love every moment of life.
most drugs whether it be lsd, weed, shrooms, etc all affect chemicals that are alread in your brain. just before you have done a drug you might not notice the things you notice after you have something to mentally attach the feeling to. so, i mean, i might have always zoned out before and thought i saw patterns and shit; but never thought anything of it. but then did 'cid and shrooms a few times and now remember those patterns as being related to the drugs and not to just nuances of the brain. ...hopefully that made sense.
It totally depends on the person and the flashbacks. My flashbacks have all been scary. Not something to rationally scared of for sure, but totally unsettling, not something I'd look forward to.
Man, I had the most insane flashback a good couple of months ago. I was in the caf in my university, you know... just doing my thing. So I was standing in the salad bar, and suddenly everything goes wrong. Colours started changing radically, the people next to me became bloody huge, the lunch lady started talking to me and it wasn't English...no sir. I picked up a piece of broccolli and could have sworn that the entire Diamond Sutra was written on it... and they I got the fear, you know... the fear. I put my tray down... walked outside the caf... lit up a cig, closed my eyes, took a drag, and it was all over. Fascinating experience though. I have never gotten "the fear" on LSD itself, it was actually rather fun.