Sion's Q stopped working.

Towards the end of my last game, sion's Q stopped working. What I mean is when I would press Q, the ability did not trigger. But, I wondered if it were my keyboard. Well, when I clicked it with my mouse, it also did not respond.

No it was not on cooldown and no I was not out of mana. Still thinking it was my keyboard, I immediately test Q in chat. And it worked just fine. I'm not sure what caused the Q to stop working, but it was towards the end of the game.