From the article I read online about Temporary Global Amnesia (TGA) there’s no real explanation for it. Sudden immersion in hot or cold water, vigorous exercise, or robust sexual activity could be triggers. Which leads me to the following hypothesis:
While riding vigorously down Mountain Home Canyon, I caught a flash of sunlight reflecting on something metallic out of the corner of my eye. Pausing to investigate, thinking perhaps one of my companions had overshot the turn and gone over the side, I discovered a poorly camouflaged, disabled alien space craft, probably a ship to surface shuttle by the size of it. My attention was observed by a creature lurking inside, who beckoned me come hither. At first he was strangely put together, a mishmash of recognizable forest animals, bear, deer, woodpecker, squirrel; but as I scrutinized him, trying to make out what I was looking at, he took the identifiable form of an attractive male human.
Exuding old-world charm, and smelling of green copy paper, he extended a hand, offering a tour of his “camper” which now did look like an Aliner.
The touch of his hand made me flush with unaccustomed excitement and I made no protest as he led me through the trees into his “camper”. Without further introduction, he began removing my stinky, sweaty bike clothes and initiated a most languid, unhurried foreplay. I was helpless to resist. Robust sex ensued.
Clearly, I could not be allowed to return to my people in this newly enlightened and totally satiated condition; so my memory was wiped clean and I was sent down the hill with the taste of his Dos Equis kiss still on my lips.
Seems as plausible as a stroke with no symptoms to me.