The defining feature of a hallucination is perceiving something, in any of your five senses, that has no external source. That sounds straightforward, but in the moment it can be genuinely difficult to tell, because hallucinations feel real. They activate the same brain pathways as actual sensory input. There are, however, reliable patterns and simple checks that can help you figure out whether what you’re experiencing is coming from the world around you or from your own brain.
What Hallucinations Actually Feel Like
A hallucination is not the same as an illusion. An illusion is a misinterpretation of something real, like mistaking a coat rack for a person in a dark room. A hallucination has no real stimulus at all. There’s no coat rack. You see a person where there is only empty space, or hear a voice in a silent room, or smell something no one else can detect.
Hallucinations can involve any sense. Auditory hallucinations (hearing things) are the most common type overall. They range from simple sounds like footsteps, knocking, or music to full voices speaking words or sentences. Visual hallucinations can be as simple as flashing lights or colored spots, or as complex as detailed scenes with recognizable people, animals, or objects. Tactile hallucinations create the sensation of touch on your skin or movement inside your body, often described as insects crawling. Olfactory hallucinations involve smelling something that isn’t there, and gustatory hallucinations produce phantom tastes.
Simple Tests You Can Try Right Now
If you’re seeing or hearing something and wondering whether it’s real, a few practical checks can help. Ask someone nearby if they see or hear the same thing. If you’re alone, try recording video or audio on your phone and playing it back. A real sound or object will show up on the recording. A hallucination won’t.
For visual experiences, close your eyes. Most real visual stimuli disappear when your eyes are closed. Migraine auras are a notable exception: the flickering zig-zag lines and colored patterns of a migraine remain visible even with your eyes shut, because they originate in the brain rather than the eye. If you see a person, animal, or object, try changing your position or moving to a different room. Hallucinated images often follow you or vanish abruptly rather than behaving the way a physical object would as you move around it.
For sounds, consider whether the voice or noise responds logically to your environment. Does it get quieter when you close a door, or stay at the same volume regardless of what you do? Does it come from a specific direction, or does it seem to originate inside your head? Voices that feel like they come from inside your skull, that no one else reacts to, or that persist in complete silence are more likely to be hallucinations.
Common Harmless Causes
Not all hallucinations signal a serious problem. Up to 70% of people experience hypnagogic hallucinations at least once. These are brief flashes of imagery, sounds, or sensations that happen in the moments as you’re falling asleep. They differ from dreams because they don’t have a storyline. You might see a face, hear your name called, or feel a sudden jolt. Hypnopompic hallucinations are the same thing, but they occur as you’re waking up. Both are normal brain activity during the transition between wakefulness and sleep.
Sleep deprivation is another common trigger. Roughly 15% of healthy people hear voices at some point, and for most of them it happens only under specific conditions like extreme tiredness or high stress. The voices tend to be mundane, neutral in tone, and often sound like a familiar family member. This is very different from the persistent, often hostile voices that characterize psychiatric conditions.
Fever and illness can also produce hallucinations, especially in children and older adults. High body temperature disrupts normal brain signaling and can cause vivid but temporary visual or auditory experiences that resolve once the fever breaks.
Patterns That Point to Specific Causes
The type and character of a hallucination often reveal its source. Knowing these patterns can help you identify what’s happening.
Migraine auras produce visual disturbances that typically start as flickering, uncolored zig-zag lines near the center of your visual field and gradually spread outward toward the edges. They usually last less than 30 minutes and almost always less than 60. The gradual expansion from center to edge is a key distinguishing feature. Seizure-related visual disturbances, by contrast, tend to last less than 5 minutes and often start at the edge of your visual field rather than the center.
Vision loss can cause a condition called Charles Bonnet syndrome, where the brain generates complex visual hallucinations to fill in for missing sensory input. People with significant vision impairment may see vivid, detailed images of people, faces, animals, flowers, or landscapes. The worse someone’s vision, the higher their risk. These hallucinations are not a sign of mental illness. The brain is essentially “filling in the blanks” when it stops receiving visual data from the eyes.
Neurological conditions like Lewy body dementia and Parkinson’s disease commonly cause visual hallucinations, often involving animals, people, or shapes that appear regularly. These tend to be recurrent and may also include hallucinations of smell or touch. If you or a loved one is experiencing repeated visual hallucinations alongside changes in thinking, movement, or sleep, a neurological cause is worth investigating.
Medications are a frequently overlooked cause. Drugs with anticholinergic properties, a category that includes certain antihistamines, antidepressants, bladder medications, and Parkinson’s drugs, can cause hallucinations along with confusion, agitation, and restlessness. If hallucinations started or worsened after beginning a new medication, that connection matters.
How Psychiatric Hallucinations Differ
In conditions like schizophrenia, auditory hallucinations tend to be more frequent, more complex, and more distressing than those experienced by healthy people. They range from occurring once or twice a week to being nearly continuous. The content often includes commands, personal insults, or hostile commentary, though voices can also be neutral or positive. Negative, derogatory voices tend to be louder than positive ones.
A key distinction: people experiencing psychiatric hallucinations are often unable to recognize them as hallucinations. This lack of awareness, called poor insight, is itself a symptom. If you’re actively questioning whether something is real, that self-awareness is actually a useful sign. It suggests you still have the capacity to reality-test, which is less common in acute psychotic episodes.
That said, insight can fluctuate. Someone might recognize a hallucination as unreal in the morning and fully believe it in the evening. The ability to question your perception is not a guarantee that everything is fine, but it is a meaningful data point.
Signs That Need Immediate Attention
Certain hallucination patterns warrant urgent evaluation. Hallucinations combined with sudden confusion, high fever, or a recent head injury can indicate a medical emergency. Smelling odors that aren’t there, particularly burning or chemical smells, can be a sign of epilepsy or other neurological conditions and should be evaluated promptly.
Voices that command you to hurt yourself or someone else require immediate help, regardless of what you think is causing them. The same applies if hallucinations are accompanied by a complete detachment from reality, where you can no longer tell what is real and what isn’t, or if the experiences are intensely frightening and escalating. A person in this state should not be left alone.
Tracking Your Experiences
If you’re having recurring experiences you suspect might be hallucinations, keeping a brief log can be enormously helpful, both for your own understanding and for any provider you eventually see. Note the time of day, what you were doing, how much sleep you’ve had, any medications you’ve taken, and exactly what you perceived. Over time, patterns emerge. You may discover your experiences happen exclusively when you’re falling asleep, or only after taking a specific medication, or during periods of intense stress. That context changes the picture entirely and makes it far easier to identify the cause.