Cerebral vasoconstriction

Cerebral vasoconstriction is the narrowing of blood vessels in the brain. A rapid fall in CO₂, for example during fast or deep breathing, can trigger it, temporarily reducing blood flow to the brain and contributing to dizziness or light-headedness. It usually reverses within minutes once breathing calms down.

The brain's vessels are very sensitive to CO₂, which normally helps match blood flow to the brain's needs. People with conditions affecting blood flow to the brain, such as a history of stroke, should seek medical advice before intensive breathwork.