Most trips involve a 4-5 hour experience, and they all end automatically and on their own. The more you cling to things or try to control what is happening the more paranoia you will feel. The point is to let go.

In a purely Buddhist sense, the experience is very interesting as an exercise of how the ego desperately seeks to assert itself when its perception of reality is altered. Paranoia, delusions, focusing on unimportant details, apprehending things that are not happening in such a way as to improperly see what is actually present (i.e., imposing your interpretation on events such that your actual view changes) and latching onto ungrounded fears.

Letting go, just "being" and letting things take you where they will, helps the experience be positive. If you go in with fears you will hold onto them when in the experience. As Timothy Leary, quoted by John Lennon, said, "Turn off your mind, relax and float downstream."