What about "Stolen Breath"

The November Witch pulls the Breath of Life from your very body. this renders you unconscious for 1d6-Con Mod. rounds. The player can be revived with a Heal check of DC 20, after which the effect ends.

That's a really rough idea, but the main idea is that it knocks you unconscious in the middle of a storm on a lake. Which is a really bad idea if you are not wearing a safety harness. This might be a bit too powerful as written, but the numbers are all really rough guesses. I hope this inspires a few things more. Perhaps the Witch needs a round for Concentration before using this ability, so that it is balanced from being used when the Witch is confident that it won't get hit.