I can totally relate. I had an amazing/life/perspective changing first experience, but then my second experience was scary; I couldn't relax, every little thing I could worry about became an irrational anxiety loop that I couldn't get out of. Since then I have come to realize through research that my problem the second time was set and setting and the amount I took was too small (both of these experiences were with ayahuasca).
One other thing I am extremely scared of is having an abduction experience! Just writing about it is making me paranoid and scared.
(There's a lot more to this, but am not in the right frame of mind to elaborate.)
I think that the main issue I'm having is my first time was so amazing, and was exactly what I hoped and worked/prepared for that due to the ambiguity of DMT experiences I actually scared I won't have another experience like that again. I actually have some changa, that I made for the first time last week, that I am just itching to smoke, but am afraid to at the same time.
I guess I just wanted to say that I understand where you're coming from, and am also grateful for a discussion in which to express my own fears.
"So it was that Dreamer put a tree at the center of the universe and from that tree were born time, space, individuality, conflict, sex, and death. Of course it is no coincidence that these are the ingredients of a good yarn and the first one the tree spun is still one of the best: boy meets girl, boy loses girl, boy gets girl back. Since then, every time a seedling sprouts, dozens of new stories sprout with it, so Dreamer hasn't been bored for a moment." -from the book "Plant Spirit Medicine"