NOT A STROKE, BUT A MIGRAINE: This doesn’t surprise me. I once had an optical migraine, in which the left 2/3 or so of my visual field was obscured by what looked like ripples in clear water. I thought it might be a stroke, and I went to the ER where they diagnosed it pretty quickly and told me that it wasn’t that unusual. Afterwards, I talked to several people I knew who’d had that experience, though I’d never heard of it.