Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

The drowning mechanic is not the same as the Drown spell. Due to technical limitations, I've generally avoided trying to make Drown work as in PnP, since our inability to reliably track whether a creature was trying to save the victim would likely make it just a fancy, delayed save-or-die. Didn't like that idea too much.

What you're encountering in the Corpse Forest isn't exactly either of those, though. First, a recap of the drowning rules:

When you're fully underwater (which is mechanically only implemented on a couple of DM maps), you're able to stay submerged for a number of rounds equal to twice your CON score (unless you're amphibious/breathless for any reason, in which case the timer never ticks). For instance, if you've got 20 CON, you can stay underwater for 40 rounds, or 4 minutes. For the record, you're also unable to cast any spells with verbal components while you're holding your breath.

After those 40 rounds have expired, you start making CON checks (not Fortitude saves!) each round, starting with a DC of 10. The DC then increases by 1 for every subsequent round you've spent underwater, and when you inevitably fail the check, you start drowning, and thus drop to 0 HP. This will happen very quickly, because most characters' CON modifiers give them a 25% or greater chance of failing on the very first round. If you stay submerged and non-amphibious for another round (i.e. nobody saves you with a Water Breathing or a Teleport or something), you drop to -5 HP. And the round after that, you die. It's worth noting that no form of healing will prevent you from dying after 3 rounds of drowning: Someone else has to either make you amphibious/breathless, or get you out of the water, in those 3 rounds.

Now, you may have noticed that the Corpse Forest is primarily inhabited by Drowned. This is a special kind of undead creature, which exudes a drowning aura. That aura fast-forwards through the drowning mechanic, making you immediately start making CON checks to hold your breath. Needless to say, this is extremely dangerous to unprepared combatants, as most PCs will only stay conscious for a couple of rounds before succumbing to the aura's effects and subsequently dying. It's especially dangerous to spellcasters, as they not only tend to have the lowest CON scores, but they also lose most of their spellcasting unless they've prepared silent spells, so they can't fight back or evade in any meaningful capacity.

That said, I've noticed a couple of possible bugs and oversights that might be causing drowned PCs to get stuck in a weird undead state, neither alive nor properly dead. And somehow one of the bugs I fixed back then has cropped back up, too...

Thank you for the explanation. I still do not know why my character succumbs to drowning aura with an immediate loss of 150% of his hit points. He has a CON of 26 before Raging.

Cheers!
MrSmith

try and use Spell Water Breathing