One morning, I successfully convinced myself that I did not exist. To be fair, it was early morning, I was tired, and I didn't want to get up. So I thought, "Oh, don't worry, you don't have to get up, because you don't really exist." In my tired state, this seemed perfectly reasonable for about five minutes. (After a short snooze, I did remember that ignoring reality doesn't make it go away, and I had to get up anyway.)
An earlier morning, I forgot that movement was possible. The alarm went off, and all I could think about it was "That noise is so annoying." It took me ten minutes to remember that I could reach over and turn it off, and another 30 seconds to remember that I had set it deliberately, because I had to get up at that time.
We, as people, like to think that we're reasonable and rational all the time, but sometimes we're clearly not. Psychologists point to a long list of cognitive biases discovered over the years. We're self-serving, seeing ourselves as better than can be warranted by the facts, we're prone to believing in consistency, ignoring all evidence that we've changed over the years, and we hate to admit it when we don't know something, preferring to just make something up and claim it to be true. A psychology student made an entertaining song describing many of the cognitive biases discovered over the years.
On top of this, we experience altered-states in which our thinking is way different than normal. Sleep and tiredness, as we began with. Drinking. Meditation. And we need to sleep, or our brain deteriorates and we die.
Often, altered states leads people to accept strange ideas, and then the various cognitive biases prevent them from ever rejecting these ideas again. Like UFO-abduction belief. There are many altered states in which other people seem distorted, most notably temporal lobe epilepsy. People experiencing temporal lobe epilepsy often experience profound religious experiences, or, if not particularly religious, perceive people around them to be aliens. Having recovered, self-consistency bias (with a slight touch of self-serving) leads them to conclude that they really were abducted by aliens and that anyone who says otherwise is a filthy liar. (Or that they really did speak with God, and what he really wants is for them to open a taco stand or whatever. And again, anyone who claims otherwise is Satan's puppet.)
I'm not sure what to do about this, but even knowing that it exists and is possible is a big defense. Just because you hear weird noises in your house at night, it doesn't make it haunted. Your vivid experience in which you teleported to Mars and learned the true nature of the universe may have just been a totally kickass dream. (Though, even if it didn't happen, that may make an entertaining novel for you to write.) I probably have some false beliefs, but I don't readily know what they are.