I must admit that it would shake my foundations if this was all a case of deception/ self deception.
Let me start by saying I do believe in genuine private revelations and their role in the life of the Church.
Throughout the ages, there have been many so-called 'private' revelations, some of which have been recognized by the authority of the Church. They do not
belong, however, to the deposit of faith. It is not their role to 'improve' or 'complete' Christ's definitive Revelation. And we should never forget that the Church never imposes on Catholics the obligation of believing anyone's private revelations, even those of the great saints.
There are, and always have been, many false events. These always seem to exhibit one thing in common, that they always are somehow centered on the importance of the visionary. Some, however, are a little more difficult to spot. And that is where meticulous discernment comes in.
But there is no doubt that in assessing the validity of private revelations it is absolutely imperative to use great caution and deeply discern them. Many spiritually hungry people are all too eager to leap in acceptance of almost any report of a supposed supernatural visitation, regardless of whether the occurrence has problematic elements to it which may be in violation of doctrinal elements of Catholicism. Christian faith cannot accept 'revelations' that claim to surpass or correct the Revelation of which Christ is the sole
fulfillment. In her autobiography, St. Margaret Mary said Our Lord told her: "Listen, My daughter, and do not lightly believe and trust every spirit, for Satan is angry and will try to deceive you." Good advice indeed (if Our Lord really said that to her - there's my discernment).
We absolutely must deeply discern before accepting any
private revelation as bona-fide, because as you point out if one day you are confronted with the falsity of it, the price you will pay will be great regret.