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 grace 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.
It is important to note that this effect is hard coded to be resisted by Mind Affecting immunity, even when this is beyond any sense of reason to be so. Changes to spells.2da, the script, or elsewhere will not alter this immunity effect. A few effects such as the Assassin's Death Attack have been hard coded to bypass this immunity.
EffectParalyze is used to apply the paralysis effect, and has the options for a save DC to break out and what type of save is done.