Stories of extraterrestrial excursions and jaunts onto alien spacecraft are not unheard of and yet people quickly discount them as liars or attention seekers. What about those people that truly believe something occurred even when in all likelihood nothing happened? Well, to answer that question it is necessary to understand the mechanics behind any occurrence that you might want to say happened.
A common occurrence in which a person might have a hazy recollection of a particular event is any alcohol induced stupor. Often individuals in such a state are not in any mind frame to recall copious amounts of details or even recite the events of the evening post consumption. Should you, the next morning, remind a friend of their crazy antics that they have have lost memory of, they would mentally do three things as you reviewed the bacchanal of the night previous.
The first thing they would do is make a plausibility judgment on the information you are telling them. Should your friend have an extreme fear of snakes, informing them that they were intertwined with your friend's pet boa constrictor and enjoying it, they might have reason to doubt. However, should you tell them that they engaged in typical college party festivities, such as a fierce game of beer pong the plausibility factor would be satisfied. In the case of our little green men visiting compadre, if they are apt to believe in alien excursions prior to their experience it is not unlikely that they would accept alien abduction as a plausible occurrence.
The next involves self-insertion into a narrative of what happened. In the case of our booze guzzling buddy personal if he vaguely "remembered" playing the game of pong when it never happened but was able to talk a little bit, maybe substituting information from pong games past into the newest endeavor, thus making the experience personal. By personalizing it the friend has now created a story to go with the false occurrence and should someone grill them about their crazy night, they would be able to recount the pong playing insanity. Similarly, our alien solicitous friend should create images and other problematic artifacts of other interactions to go along with the strange experience that they are now in the process of constructing.
Finally, the full acceptance of a memory relies upon a source monitoring error in that, in the case of our tipple tilting terror, complete acceptance of our fibs about pong playing due to social pressure, our suggestions, and personal claims of memory (his experience of feeling like he played) he will lose the source of the information as from our telling him he played pong when in fact he fell asleep on the couch after his fourth shot of tequila and did not wake up until morning. His loss of the source will lead him to believe the night held a great deal of pong madness despite his lack of coherent memories surrounding it. Similarly, our alien encountering confidante could easily have a similar experience, or may they had a dream about aliens and convinced themselves it happened. Either way, they remember abductions.
Now that the methods and processes underlying the false memory of alien abduction have been parsed out quickly if not hurriedly, I will simply state the effect of hypnosis on recovering accurate memories. You can't, it won't, and it doesn't work. Hypnosis, when the attempted purpose is to recover memories, increases rates of false recognition while subsequently increasing rates of personal confidence in the memories recovered. Not only will our bungled up booze boy believe our lie even more fully, but over time he will be so sure it happened that he will be telling his grandchildren about the story 50 years later, should his liver survive. Consequently, the same is true for alien abductions and hypnosis, in that, using hypnosis will further engrain the memory into an individual without lending any true insight into what their memory is. Memory is a reconstructive process and hypnosis aids in allowing any suggestion to be the right one, destroying any hope for accurate retrieval of memories.
Overall, hypnosis + false memory of alien abduction + semi-convinced alien believer = hardcore convinced alien fanatic with a stellar abduction story.