A Fed spokesman passed it off as dehydration at the end of a long speech, but a medical friend who viewed the video of Yellen's odd behavior, at the request of EPJ, says he suspects it might have been a Transient Ischemic Attack.
He cautions that his suspicion may be off given that he did not personally observe Yellen and question her at the event and has not run any follow-up tests, but he said, from the video, it appears the actions of Yellen appear more consistent with TIA than dehydration.
Here's what WebMD has to say about TIA:
A transient ischemic attack (TIA) happens when blood flow to part of the brain is blocked or reduced often by a blood clot. After a short time, blood flows again and the symptoms go away. With a stroke, the blood flow stays blocked, and the brain has permanent damage. Some people call a TIA a mini-stroke, because the symptoms are those of a stroke but don't last long.-RW
A TIA is a warning: it means you are likely to have a stroke in the future. If you think you are having a TIA, call 911 or other emergency services right away. Early treatment can help prevent a stroke. If you think you have had a TIA but your symptoms have gone away, you still need to call your doctor right away.
Symptoms of a TIA are the same as symptoms of a stroke. But symptoms of a TIA don't last very long. Most of the time, they go away in 10 to 20 minutes. They may include:
Sudden numbness, tingling, weakness, or loss of movement in your face, arm, or leg, especially on only one side of your body.
Sudden vision changes.
Sudden trouble speaking.
Sudden confusion or trouble understanding simple statements.
Sudden problems with walking or balance.