Paralysis: Paralyzed individuals are unable to move or take actions of any kind and are considered prone. A paralyzed NPC with 4 HD or less will be killed instantly (like sleep) if successfully hit in melee, called a coup de gras in NWN.
Breaking out of paralysis
Usually, for spells, you can break out of paralysis (see Hold Monster for example) every round, based on the original spells save DC. The save is based on the original save you had to take.
Paralysis for other abilities also use the 3.5E rules for breaking free. Once you break free the effect ends and you can act as normal.