He was preoccupied with making it obvious how sleepy he was because he actually was sleepy, and actually had been woken up, and that really shouldn't have been a novel idea, but there they were.

"The lake?" He leaned back as Rin leaned in, eyebrows knitting together in mild confusion. "Right now?"

So there wasn't any dawning realization, nor was there any excitement or him leaping out of bed to run off to the lake. That would probably all hit him once they were there, with the rush of adrenaline from breaking the rules, to getting to swim with his friend out in the cool moonlit water.