Bizarro is brought to you today by Hallucinating 101.
Hallucinating can be fun as long as it isn't dangerous. There are many recreational drugs that will cause hallucinations, some are safer than others, of course. As a matter of legality, I'm not recommending any of them. Hallucinating during a fever is no fun, mostly because a fever that high is quite painful and can kill you. Sleep deprivation can also cause you to see things, as any parent of a newborn will tell you.
Turns out it's fairly easy to cause a person to hallucinate. I'm not going to get all grammatically literal about it, but some optical illusions can reach the level of a sort of hallucination. If you've ever been in those fun house places that are built with everything all catawampus, and balls appear to roll uphill and water pours sideways, that's pretty close for my money.
Our brains are actually geared toward this sort of thing. We (and most other creatures) have evolved to spot patterns and make some version of sense of them, which helps us survive. For instance, it is much safer to see a shadow and think it is an intruder than to see an intruder and assume it is a only a shadow. This is one reason people so regularly see faces in random shapes, like the image of the Virgin Mary in your toast or the bark of a tree. One of my favorite examples of this is this image of Jesus in a dog's behind. Wow.
Here's a good one that has nothing to do with religion.