The reason why travel is possible after sexual climax is that the physical body becomes relaxed and the spiritual is energized. After sex, the physical body feels tired and relaxes.  The spiritual body is energized.  The physical body desiring rest or sleep then usually feels tired and sleep comes easily and quickly. 

During this quick and deep sleep, the spiritual body being energized finds it easier to travel. 

This is why astral travel after sex is preferred over other methods of astrally traveling; the physical and mental aspects of your life force on this earth drop off into a deep sleep.  The spiritual, however, then travels while you are asleep.  The fact that you do not remember sleeping or falling asleep is significant in that this indicates a period when you were out of your body and therefore did not remember the body in sleep.

First, assume you will astrally travel and remember the event.  Concentrate on focusing your travel destination to your higher self. 

Focus the direction on travel.  Once the higher self is met and remembered or properly visualized, then this is as much more effective way of addressing the travel experience.  So perhaps in quick order, there are conduits, you may think of them as pathways diverting from a clearing in the forest.  Each path leads to a different destination and one can not see where it goes, but has a general feel for the direction and the type of scenery or views to be obtained form it.  However, by relying on your intuitive senses, one may discover the particular path that is most earnestly desired.  This analogy is how pathways or conduits work.  Your desires that your soul intuitively feels lead it in the proper direction.