Talk about a slumber setback.

It’s not just when you go to bed, but how your head hits the pillow that can significantly influence several aspects of your well-being, from breathing and digestion to spine alignment.

And while many prefer two pillows to get a good night’s rest, some people may want to reconsider that position for their health.

Propping up the head with an additional pillow may provide temporary relief from sleep apnea, acid reflux or sinus pressure.

But a 2026 study found that this method may not be the best for those with glaucoma, a group of diseases that cause pressure to build up inside the eyeball, damaging the optic nerve and causing permanent vision loss.

Published in the British Journal of Ophthalmology, the study found that two stacked pillows with an elevation ranging from 20 degrees to 35 degrees were linked to increased internal eye pressure, or intraocular pressure (IOP), in two-thirds of glaucoma patients.

The findings surprised researchers and other health experts, as it challenges standard guidance.

“Since it has been known that lying down to sleep increases IOP, some clinicians have recommended to their patients that they should sleep on multiple pillows to increase the height of their head over their heart,” Dr. Thomas V. Johnson, of the Wilmer Eye Institute at Johns Hopkins University, who was not involved in the research, told MedPage Today.

The research team also noted that younger participants — those under the age of 44 — had significantly greater intraocular pressure increases than their older peers.

The researchers believe that elevating the head inadvertently causes the neck to flex and the jugular veins to constrict, which blocks fluid from draining properly from the eyes.

This theory was confirmed when a separate test was conducted on different volunteers. There was increased blood flow into the jugular veins of those in the high-pillow position, meaning the veins were constricted.

While the study looked at the elevated head position of back sleepers and its effect on IOP, side sleepers weren’t evaluated.

Previous research has linked lower pressure to using wedge pillows or raising the top end of the bed, but the jury’s still out on which position is ultimately best.

“We do not yet know what sleep position may be optimal for patients with glaucoma, if any,” Johnson said.

Sleep specialists also advise against more than one pillow, as it allows for a more natural alignment of the spine and neck, lowering the risk of pain and discomfort.

However, dozing with a second pillow can come in handy in some situations, as some experts recommend putting one pillow under the knees and another under the neck to support proper spinal alignment and reduce back pain.

Johnson recommends whichever is most comfortable for patients, “as there is not strong enough evidence from high-quality clinical research to recommend otherwise.”

But since eye pressure is affected by body position, the difference may be most notable in those with advanced glaucoma or low intraocular pressure throughout the day.