Internal hallucination from Diphenhydramine

Internal hallucination is a visual effect defined as the perception of hallucinated imagery that occurs exclusively within an internally generated mental landscape, typically only visible with one's eyes closed or in very dark environments. Unlike external hallucinations, which overlay or integrate with the real visual environment, internal hallucinations exist in their own self-contained space — a kind of inner theater of the mind where scenes, landscapes, entities, and narratives unfold with varying degrees of vividness, complexity, and autonomy. The experience shares qualities with dreaming, except that the experiencer typically remains conscious and aware that they are hallucinating.

At lower levels of intensity, internal hallucinations manifest as relatively simple imagery on the backs of one's eyelids — fleeting snapshots of faces, landscapes, objects, or abstract forms that do not take up the entirety of the visual field and are clearly distinct from their dark background. These images may be still or slowly moving, and they often respond to the person's thoughts and intentions, shifting and morphing in response to changes in attention or emotional state. As intensity increases, the imagery becomes more vivid, detailed, and expansive, gradually filling more of the visual field and taking on greater realism and narrative complexity.

Internal hallucinations are most commonly induced under the influence of high dosages of psychedelic compounds such as DMT, ayahuasca, psilocybin mushrooms, LSD, and mescaline, where they are considered one of the signature visual effects of the deep psychedelic experience. They also occur with dissociatives like ketamine and DXM, particularly at higher doses that produce "hole" experiences, and with deliriants such as diphenhydramine and datura, though the character of delirium-induced internal hallucinations tends to be darker and more confusing. Certain hypnagogic states, lucid dreaming, and sensory deprivation can also produce internal hallucinations without substance use.

The content of internal hallucinations is remarkably diverse and can include recognizable scenes from one's life and memory, fantastical landscapes and architectural structures of impossible complexity, encounters with autonomous entities that appear to possess their own intelligence and intentionality, symbolic or archetypal imagery, and abstract patterns of extraordinary beauty and intricacy. Many users report that the hallucinations seem to carry meaning or convey information, as though the visions are organized around themes relevant to the person's psychological state, life circumstances, or existential questions. DMT and ayahuasca are particularly noted for producing internal hallucinations with a consistent quality of feeling profoundly meaningful and populated by apparently intelligent beings.

At their most intense, internal hallucinations can become fully immersive experiences that are indistinguishable from waking reality in terms of their vividness and detail. In this state, the person may feel as though they have been transported to an entirely different world, complete with consistent spatial geometry, vivid colors, detailed textures, ambient soundscapes, and sometimes even tactile sensations. The hallucinated environment may feel more real than ordinary reality, and the experience of navigating these spaces can be profoundly moving, terrifying, or awe-inspiring. Users sometimes describe the experience as visiting other dimensions, communicating with alien intelligences, or witnessing the fundamental architecture of consciousness itself.

Internal hallucinations are closely related to several other visual and cognitive effects, including geometry (the patterns and structures that underlie hallucinated imagery), external hallucinations (their open-eyed counterpart), and scenarios and plots (the narrative structures that organize hallucinatory content). The vividness and character of internal hallucinations are strongly influenced by set and setting, with calm, dark, quiet environments and intentional, meditative mindsets tending to produce the most detailed and coherent visions.