Transient global amnesia related to migraine?

72 year old male. Frequent (almost weekly) episodes of temporary amnesia began about 1 year ago and occur day or night. Sometimes preceded by stress, not always. Before an episode, food tastes different. Begins with sudden onset of nausea. Jumps up, walks halfway across room, stops and blurts out a few words in agitated tone of voice, then starts making chewing motions with his mouth for 30 seconds or so. Sometimes trembles in fear. Does not respond for a minute or two, then asks a question such as, "Do we live here?" but cannot process the answer. Gradually starts remembering again and can add details. After 20 minutes or so has regained senses, but may remain confused and slip in and out of amnesia several times during the next day or so. Says he felt like he was dying but can't remember anything that happened while he was "out." Afterward, reports that food tastes unusally delicious. Has had laparoscopic gall bladder surgery. Had MRI, ruled out stroke. Neurologist told him to avoid tranquilizers and sleeping pills, which he does. A long time ago an optometrist, after looking into his eyes, told him "classic migraine." No headaches, though. Has high blood pressure controlled by medication, takes synthetic thyroid. General health good.

What to do? These episodes are frightening. Worry about long-term effects. Has had a gradual worsening of memory over the last few years. Appreciate any advice you can give.