Believe me when i say, it's all in your mind. Whenever you feel paranoid, it is just because you didn't come into the high with a clear, positive attitude. Does that make sense? You were probably worried about something, or something was on your mind that triggered the paranoia.(ie your scared you might get caught by parents, cops, etc.) It takes some practice to counter this, because you have to just clear your mind and just remember how good it feels to be high and you will truly enjoy the experience.

i kno this sounds gay, but i love weed