You feel an odd tingle all over your body, but especially in your legs. You wonder if its some kind of muscle cramp or maybe you tweaked your neck somehow?
You get to your feet, feeling a little unsteady. You take a few steps, but walking feels a little strange. Just then a light breeze blows through the yard and you feel the air against your skin. It causes an extra tingle where your swim trunks are. You look down and notice your swim trunks seem longer than they used to be and seem to be clinging tighter to your legs than normal. You try to adjust the trunks, but they wont budge and you can't seem to get your fingers under the waistband.
You are wondering what is going on when you realize the water suddenly seems terribly inviting; you have to resist the urge to immediately dive back in the pool. You start to panic briefly before realizing the obvious: this is very much like how Lydia described the beginning of her transformation. But why are you changing? Yes, water plus swimsuit is apparently a transformation trigger, just like Lydia. But you never wished to become a merman.
Is Lydia's "condition" contagious - some kind of magical STD? Have you been tricked by the genie somehow, or otherwise have some deep hidden desire now causing your transformation as part of your original wish? You realize you're not even certain if you're transforming into a merman or a mermaid.
You can now truly sympathize with Lydia, knowing you are changing but not why or exactly into what.
A towel sits nearby to dry yourself off and delay whatever change is happening. Then you could call Lydia and tell her what's going on. But the water continues to beckon you to return to the pool. Maybe you should just get it over with and find out the extent of your transformation?