I had almost the exact same experience over Memorial Day Weekend while on vacation this year. I was waiting for friends to get ready to go to brunch and started to read my kindle but I could only see part of the words. I have had ocular migraines in the past but long ago and I thought this was too much caffeine and no food. Soon after in the car , just as you describe, I saw some flashes of light and then developed a headache. I rarely get painful headaches so this was a bit odd though not extreme. We got to the restaurant and were talking and all of a sudden I was unable to speak the words in my head out loud. I knew what I wanted to say but I could not say them correctly. Like you, I know the symptoms of a stroke and I was able to tell my husband and friends to call 911. We were close to the hospital so they drove me. Once there I passed most of the stroke test and my speech improved but I still said some incorrect words — mattress when I meant Masters. Long story short tests all normal — and they diagnosed it a probable TIA. I recently got a masters in health and read up online and decided I was not going to have a full stroke and checked myself out against drs recommendation so I could return home to the my Drs and hospital. I was seen the next day and the Neurologist said — You did not have a TIA, you had a migraine with aphasia. I was astonished. My sister suffers from days long, incapacitating migraines with severe pain, sensitivity to light and nausea. It never occurred to me that I was having one. I felt a little silly going to the ER given I have zero risk factors for a stroke — I also eat a vegan diet and exercise. But the neurologist said I absolutely did the right thing. Now that I know I can get these I do not need to go to the ER but I needed to the first time. He confirmed the symptoms mimic a stroke and you don’t take a chance with a stroke.