You put the ring on and wade out into the salty water. The mermaid swims out ahead of you, then turns back to watch as you slowly immerse yourself. Without the adrenaline pumping through your body when you though you saw somebody drowning the ocean waters feel a lot colder.
Keeping your mouth shut tight against the salty wetness you continue a bit farther out, treading water now that your feet no longer reach the sandy bottom, teeth chattering behind your sealed lips as the ocean breeze against your wet, bare skin poking up out of the water chills you as much as the thought of voluntarily inhaling water. Sure, the mermaid is pretty and seemingly magical and all - but over the last few hundred million years evolution has managed a pretty bang-up job at this thing we call the need for self-preservation.
The mermaid does a little somersault at the surface, flicking water at you with her emerald tail. Before she can ask you if you're scared, though, you take a breath and dive under the water to show her that you most definitely are not.
Once underwater you open your eyes, still holding your breath - the instinct to not drown is pretty strong. The salt water burns your eyes for a moment, but after blinking a few times the view clears and the irritation stops. Maybe it's your imagination, but you think you can feel a bit of warmth coming from the finger with the ring. In fact, the water temperature itself seems to be less cold than you were expecting and remembering.
The mermaid swims laps around you, moving effortlessly through the water. You're still getting used to the fact that you can see as clearly as though you were wearing goggles, even though you just as clearly are not. She smiles, and you try to smile back - sending up a line of bubbles as some of your precious air escapes through your lips at the motion.
"What are you waiting for? Relax. Breathe." The mermaid says, her voice carrying just fine underwater with no air bubbles of her own. Of course, her lungs are full of water, so of course she can talk fine. She swims up behind you and gently gives you a reassuring stroke across the back, wrapping her tail around your waist. "Go on. Take a breath."
You nod once and expel the air that you've been saving, watching the bubbles drift up to the surface of the water where the sun shines brightly above, the ripples on the water casting a lovely play of light and shadow here in the shallows. When you try to inhale however, your body protests and you instinctively try to push up to the surface again. Air! Oxygen! Help! Don't want to die!
The mermaid's hands clamp down on your shoulders, holding you in place. You kick frantically, struggling to break free, but her grip is strong and you can't escape. You reach for the surface with everything in you, the most primal parts of your brain knowing that this is suicide! Finally, when your lungs are on fire to the point that you cannot bear it any more...