One of my favorites YouTube Errors is by designer Brittany Broski, who complained to drag queen Trixie Mattel (who was busy at the time giving the online star a makeover): “When I close my eyes, I can’t see.”

It’s hard not to laugh at Trixie’s incredulous “Well…”, considering we all know the world goes dark when we lower our eyelids.

Except… right? Although we clearly cannot “see” the real world when our eyes are closed, many of us begin to notice patterns, shapes, and colors when our retinas are deprived of light.

Why, how common is it and what does it mean?

According to health information site HealthlineThese are called “closed-eye hallucinations.”

These are technically hallucinations because, when you close your eyes, you can’t see – the visions come entirely from your brain.

Common “closed-eye hallucinations” include swirling shapes, pixel-like squares, seemingly random objects, and even flashing lights.

Mine often look a bit like the ever-changing Windows 98 screensavers and it never occurred to me that not everyone sees them.

These come from phosphenes, healthcare providers Cleveland Clinic explains, which create “flashes of light with or without structure that you see when no real source of light enters your eye.”

They are most often present when there’s pressure on your eyes (I sleep with my face buried in a pillow, so that makes sense) ― but they can also come from your brain or retina.

Delusions “may or may not” be a sign of medical problems, Cleveland Clinic said – however Healthline assures us that“Closed-eye hallucinations are usually not cause for concern.”

They can sometimes occur after a blow to the head, following retinal or neurological disorders, due to chemotherapy and radiotherapy, or as a withdrawal symptom.

They can also appear when you cough or rub your eyes and even reveal low blood pressure.

“If you see phosphenes frequently and have other symptoms that worry you, such as double vision (diplopia) or blurred vision, you should see an eye care professional, such as an ophthalmologist,” Cleveland Clinic Actions.

“If you know you have diabetes or see floaters associated with phosphenes, you should also see an eye care professional.”

Healthline adds that “if closed-eye hallucinations are so severe that they cause insomnia or anxiety, consider seeking medical attention.”

However, the majority of cases are nothing to worry about.