Scuba

Mimi McMillan has been drowning for quite some time. She doesn't know how it started and she honestly can't even remember how she found herself in the water.
No one's noticed her slowly sinking that much she knows for sure. Either that or no one cares quite enough to look beyond the surface. That little possibility is enough to make Mimi tie an anchor to her leg and give into the descent.
But somewhere up on the surface maybe there's a little lifeboat and a diver wearing an oxygen tank with enough air in it for the both of them.