More seriously, reality is surprising fragile. Individual neurons encode a lot of information. Small neural circuits, when activated, can cause you to experience realistic scenarios. If you have a microsleep or your consciousness becomes disconnected from your sensory inputs for whatever reason, neural circuits associated with reality can keep firing but with no input from the 'real' world. So you can experience things that don't happen.

I'm not sure if you've ever experienced this state of consciousness, but if you're in between sleeping and awake, the brain will easily integrate external inputs into a backstory. For instance a loud sound will become a gunshot and your brain will work backwards in time to construct a reality in which the sound makes sense.

What's really upsetting is the idea that this might happen a lot. Or always. Our brains could be making all of reality up and we'd have no way to know. So your glitch could be that this time you noticed something was off when usually you do not.