You have never had a dream like this, but that it what it must be. There's no way it can be real, right? Convinced, you decide to enjoy the fantasy for as long as it lasts. You swim around the lagoon, familiarizing yourself with your unfamiliar form, surprised at the ease with which you acclimate to the water, breathing with gills, and having a fish-like tail. You dive a bit, then gathering speed, breach high above the water in the starlight, entering the sea with a nearly splash-less dive.
As you flip underwater in glee, you hear a few titters in the distance, and spot the mermaids from earlier. Feeling a slight throbbing in your loins, you flip your tail with expertise and speedily chase after them. After a mad version of tag through various offshore coral reefs, the mermaids finally lead you to a beautiful underwater cavern, where the starlight seems to reflect off every surface giving it a luminous glow. Here the chase ends, as the mermaids surround you. Gently, lovingly, they bring you to a fever pitch, drawing out sensations you never imagined possible. The rest of the night is spent in a strange underwater ballet of love-making, first with one mermaid, then another. Although you have no idea what a merman would do for sex, the mermaids seem quite familiar with the process, and easily guide you through it. There is no conversation, only tender caresses until you finally fall asleep, tail intertwined with those of the mermaids in a glorious floating heap.
You open your eyes to see a seagull careening above in the pre-dawn light. You can feel the grit of the sand beneath your entire body, down to your feet. "It really was a dream," you think to yourself, with some measure of regret. However, the next second you freeze, then sit up. You are human and on the beach, but you don't have a stitch of clothing on you, and, looking down, you realize you are...completely male. Maybe it wasn't a dream after all.