there is no scientific evidence or research to suggest that octopuses experience nightmares or have the capacity to dream in the same way humans do. Studying the dreaming experiences of animals, especially those with vastly different neurobiology from humans, is challenging.
Dreaming is a complex cognitive process that involves rapid eye movement (REM) sleep in humans and many other animals. While REM sleep has been observed in some birds and mammals, it is not clear whether octopuses experience this stage of sleep.
Octopuses have a highly developed nervous system and display remarkable cognitive abilities, but their brain structure and functioning are quite different from vertebrates, including humans. They lack a centralized brain and instead have a distributed nervous system, with a significant portion of their neural tissue located in their arms. Therefore, it is challenging to draw direct comparisons between human dreaming and potential dream-like experiences in octopuses.
Until more research is conducted, it remains uncertain whether octopuses have dreams or experience any dream-like phenomena. As with any animal's internal experiences, understanding their subjective experiences, if they exist, is currently beyond our scientific capabilities.