Suffocating

During combat or under similarly stressful circumstances, you can hold your breath for a number of combat rounds equal to your Might score (minimum 1 round). At the end of each combat round after that, you take 1d6 damage while holding your breath.

Out of combat, you can hold your breath for a number of minutes equal to your Might score. Being unable to breathe after that time counts as a stressful condition, causing you to run out of air as above.