I consider something like the
Janken Rock-Paper-Scissors robot as a way to explain how Deja Vu is formed in the mind.
The robot basically adapts an output in milliseconds after identifying the result of an input. The result is a game of rock paper scissors where the robot appears to win every time.
In the case of the Deja vu it would be like observing an event and while that observation is being recognised, a feedback of that observation is being looped back into the observation itself. (A feedback loop)
It's possible that it's actually a form of
Synaesthesia which is why it's not registering as epilepsy.
I'd be interested in two experiments in this particular instance:
One involves asking the guy to wear VR specs that apply two different video feeds, one to each eye. Then changing the timing of the video so that one or other eye is one millisecond ahead of the other. This could possibly be used to identify if it's hemisphere related (where such a feedback loop requires both hemispheres to function)
The other would be to ask the guy to use a BCI (Brain Computer Interface) to control a character in a virtual world. If he did so for a duration, it's possible that he might be able to retrain his brain not trigger the effect that makes him uncomfortable.