A 55-year-old construction worker presents to the hospital after collapsing on the job. He is a smoker of 15 cigarettes per day but has no other medical history. Upon awakening at the construction site, he experienced slurred speech, dizziness, and temporary symptoms on the left side of his body. These symptoms had resolved by the time he arrived at the Emergency Department. Imaging revealed a proximal stenosis of the right subclavian and carotid arteries. EEG results were negative for spike activity. What is the most likely diagnosis based on this clinical presentation?