At first you can't believe your eyes. The next obvious assumption is that you are still dreaming. Therefore, naturally, you pinch yourself.
"Owww!...oh shit."
You're not sure what to do at this point, short of panic. You can't just slide into the ocean and disappear, you have no gills anymore. As for returning to your old life, who would believe that you magically turned into a guy overnight? In an official sense, you don't exist, and you have no way of accessing anything from your former life...your credit cards, your bank account, even your car keys are lost at the bottom of the lagoon somewhere. Where are those damn mermaids?
At first, you get to your feet and run up and down the beach, looking desperately for a flash of a scale, the splash of a fin, anything in the water. However, there is nothing but the gentle ripple of the waves shining in the rising sun. Quickly losing hope, you run into the waves and dive into the water. While you are human and still required to breathe air, your body seems to have changed dramatically. Your swim speed has increased by a huge amount, and you find yourself cutting through the water with ease. You are even able to hold your breath for long periods of time, much longer than a normal human. Your male body is sleek and streamlined, almost as though it were designed with swimming in mind.
Nevertheless, you are too frantic to appreciate this. Every hundred yards or so you swim further from the beach, you dive as deep as you can, looking for any signs of the mermaids, but come up empty-handed. You are so engrossed in your search that you do not notice how far from land you are, which is now a mere sliver on the horizon. You don't even bother looking around anymore when you reach the surface, but simply grab a quick breath and continue your underwater scanning as the ocean gets deeper and deeper.
As you are finally beginning to run out of stamina, you force yourself to make another dive, this time pushing yourself as deep as you can go. Seeing nothing but dark blue expanse, you finally begin to despair, and float there motionless for a bit. Lost as to your next step, you don't notice something approaching you from behind. Suddenly, feeling a faint ripple in the water, you whip yourself around.
Both you and your stalker let out a mouthful of air in surprise. The loss of your air makes you flail for the surface, but not before you catch a glimpse of a dark wetsuit with scuba tanks. Finally breaking the surface, you gulp air greedily, then look around to see a red and white diver's flag a little ways away with a kayak tied to it. Just as it registers that you are not alone, the diver surfaces next to you and, grabbing your arm, pulls you towards the kayak. You think about resisting, but at this point you have no plan. The mermaids are gone, and you are stuck like this without any way to go back to normal. Your old life is lost, so what is the point?
The two of you reach the bobbing kayak and grab ahold. The diver takes off the tanks in a practiced motion and heaves them into the kayak, then pulls off a pair of goggles and yanks back the hood of the wetsuit. You are dazzled by a mop of unruly short platinum blonde hair, which sparkles in the sunlight as the diver turns to reveal a tanned face with fine features and hazel eyes, eyebrows knotted in concern.
"Are you okay? What on earth are you doing all the way out here?" she asks you incredulously.