A perception in the absence of external stimulus.
Durante la noche, tuve una alucinación en la que creía que alguien me estaba llamando por mi nombre.
During the night, I had a hallucination in which I believed someone was calling me by my name.
La alucinación que experimentó durante la fiebre lo llevó a ver cosas que no existían.
The hallucination he experienced during the fever made him see things that did not exist.