Woman with Episodes of Nausea, Vertigo, Unresponsiveness and Staring spells

An 83-year-old healthy woman was admitted with episodes of nausea and vertigo that had increased in frequency over several months. Many of the episodes involved brief periods of unresponsiveness and staring spells.

Woman with Episodes of Nausea, Vertigo, Unresponsiveness and Staring spells
Woman with Episodes of Nausea, Vertigo, Unresponsiveness and Staring spells

What is the Diagnosis?