Why Do I Sometimes See Vivid Mental Images Or False Perceptions, Like Thinking I Threw My Retainer Out Or Seeing Someone Who Isn’t There?

why do i have like visions not really visions but like imagers i see. like one time i thought i threw my retainer out of the window but then i looked down and it was in my lap. anothwr time i swore i saw my friend like running toward me but in reality i was alone in my room.