Here is what Hubbard said in 1952:
Now, all this of course is—I’m just kidding you mostly. I don’t believe that you’ve been in the universe 76 trillion years. I don’t believe you have any past before birth. I don’t believe that there is any reason whatsoever for this universe to be here except some fellow called the devil or something that built it. And I don’t believe any of these things. And I don’t want to be agreed with about them. It infuriates me to be agreed with about them. [Source]Here is what Hubbard did months before his death:
As Techie points out, one of the surprising things we learned from Lawrence Wright’s epic 2013 history of the church, Going Clear, and then in even more detail in the final chapters of Mark “Marty” Rathbun’s 2013 book Memoirs of a Scientology Warrior, was testimony from Steve Pfauth, who was with Hubbard in his final years in seclusion, and who said that during Hubbard’s final months the frail old man was earnestly searching for those invisible, disembodied alien souls — body thetans — hoping to chase them away. Hubbard really seemed to believe his own science fiction at that point. [Source]So apparently it is possible to convince oneself of the verity of one's own lies. The brain has a way of reprogramming itself to believe even one's own fantasy. Could the Apostles have been victims of that?
Not likely. First, there are massive differences between L. Ron Hubbard and the Apostles, the first one being that L. Ron Hubbard had never experienced persecution or duress (if anything, he was persecuting the United States government, as operation Snow White demonstrates) and was never in a position of fighting for his life. If he had been under those conditions, he probably would have confessed.
Second, there actually is a parallel to the "liar-who-believes-his-own-lies" who was put into a situation comparable to what the Apostles were under, and that was Sabbatai Zevi. He was a Jewish occultist (he practiced Kabbalah, which is most definitely occult) who believed that he was the Messiah... and famously renounced it all and converted to Islam when put into a situation where he had to confess and die.
In conclusion, considering that the closest situation in history to someone who has believed his own lies recanted completely under the duress of death and positive temptation of total clemency, it is likely that the Apostles did not make it up but instead really did believe that Jesus Christ was risen. As to what caused that belief... is left for the reader to investigate.