Which episode of Pokemon does ash get unconscious?

It's impossible to give you a definitive answer to which episode Ash gets knocked unconscious in Pokemon without knowing more context. There are several instances throughout the series where Ash might be:

* Knocked out by a Pokemon's attack: This happens frequently in battles, but it's rarely permanent.

* Injured by a Pokemon's attack: Ash gets hurt in battles, sometimes to the point where he's unable to continue fighting.

* Overwhelmed by an environmental factor: He could be poisoned, frozen, or even simply exhausted from a long journey.

To help me pinpoint the episode you're looking for, could you tell me:

* Which Pokemon series are you interested in? (e.g. Original series, Advanced Generation, Diamond & Pearl)

* What kind of knock-out are you looking for? (e.g. Brief unconsciousness, serious injury)

* Is there a specific Pokemon involved? (e.g. Was it a specific attack or a specific Pokemon that caused it?)

Once I have more information, I can help you find the specific episode you're looking for.