Fanatic's Aegis

When dropped to 0 hp, would you discard cards in play before returning to 10 hp?

Thanks

No.  You only ditch your cards in play (and hand and trash and deck) when you're actually incapacitated.  The Aegis replaces the instance of lethal damage entirely with "set your current HP to 10, then destroy the Aegis".  (Note that this happens even if a Fixed Point is in play, which would prevent you from actually being incapacitated at 0 HP...conveniently, it also prevents you from destroying the Aegis, so you just get to go up to 10 HP with no downside, even though losing your last HP wouldn't actually kill you that round.)