It was decidedly scary. I had just logged in to post something, when the browser window closed. Then TweetDeck closed. Then the mail client dropped, and the system shut down.
“What is this? Some sort of zero-day exploit?” I’m still not sure. I swapped out the keyboard and the up-acting quit acting up; on the other hand, I’d started up Malwarebytes, and it didn’t seem happy with what it found. I’ll swap in yet another keyboard tomorrow night.
Update: Second pass, MBAM found nothing, keyboard acted silly. Q.E.D.