We now have a medical explanation as to why Los Angeles CBS reporter Serene Branson garbled her speech on air Sunday night after the Grammys: A “complex migraine,” and not a stroke.

Branson’s doctor, Neil Martin, chief of neurosurgery at the Ronald Reagan UCLA Medical Center, told Los Angeles Times that a complex migraine can mimic the symptoms of a stroke, including headache, weakness, loss of vision and difficulty speaking.

Martin received permission from Branson to discuss her condition publicly.

One of the causal theories of complex migraines is that blood vessels in the brain suddenly narrow, or spasm, and then dilate again. That re-dilation causes a headache but during the spasm phase, certain parts of the brain receive too little blood, causing the temporary stroke-like symptoms.