You're a mermaid. Due to this, the British Men of Letters found you and took you to perform experiments on and also partly because they believed you were a monster of some kind, though that wasn't true. Mermaids only ever drowned humans in self defense.

Fortunately, you were a friend of Sam and Dean. So, they made a plan to rescue you. Afterwards, they took you back to the bunker to recover, where you'd just been sitting in the bathtub for hours.

Sam walked in on you and sat by the bath, on the floor. "Feeling any better?" He asked, setting a cup of tea on the bath rim. "It's herbal."