Dr. Carol Foster poses with her new book, “Overcoming Positional Vertigo," at the CPR studios on Jan. 11, 2019.

Hayley Sanchez/CPR News

You're lying down and you turn you head slightly. Then it hits.

The room spins uncontrollably for what may feel like forever but could be as short as 30 seconds. The sensation is vertigo, and it affects millions of people.

One of those people is Dr. Carol Foster, who specializes in vertigo at the University of Colorado's School of Medicine. She’s also the author of “Overcoming Positional Vertigo," which shares her findings. Foster talked to Colorado Matters about the common phenomena.

Vertigo happens when crystals found in the ear and sense gravity fall out of place and create the disorienting illusion of spinning.

There are multiple kinds of vertigo, but to treat the most common variety, Foster recommends a number of head and body motions, including the "Half Somersault Maneuver."