The other kind of stimulus could have been an electric spark. Easy to accumulate a charge if you are wearing the right shoes and the carpet is of the right materials. People don't think about it. It is instantaneous and can affect the nervous system.

But his vacant stare and immobility really suggests something like a stroke or a TIA. Something happened to completely disrupt his concentration. It could have been a sudden wave of dizziness. (Something that has been afflicting me for 2-3 years, which I now think is a side effect of my diuretic. But the distraction is real, and disruptive.)

Edit: I got a chance to review the video clip. Too fast to conclude much about the woman's touch, but his expression was alarming. If he hadn't remained standing and balanced, I would have taken it as the mask of death.