system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we hallucinate? What's happening during it?
gpt
The portions of our brains responsible for interpreting our senses are generating their own signals or interpreting signals incorrectly. 

Sight, for example, is just the interpretation of light radiation sent as a chemical/electrical signal from our optic nerves to our occipital lobe. If, for some reason, our occipital lobe generates it's own chemical/electrical signal, we'll "see" things that aren't actually there. 

You can perform a quick "pseudo hallucination" by closing your eyes and pressing gently on your eyelids. A bunch of lights will appear. 

Other common pseudo hallucinations are thoughts and dreams.