I just had my controls become completely unresponsive for no apparent reason during an event. I wasn’t stunned (I had no conditions at all for most of the duration) but nothing would activate at all until I was downed. Movement, skills, whatever. The game was aware I was pressing keys as skills would blink but not activate, even delayed, so I don’t think it was lag (plus lag has never immobilised me before).
It was actually very much like having pressed enter accidentally and entered chat… but that was one of the first things I looked for and it wasn’t the case. The moment I was downed, things started to work again, not that it did any good by then.