He wakes up and the first thing he notices is that his skin feels different. Touching his hand to his arm he realizes that he's hairless and his skin is softer. It feels really nice to touch and be touched actually. And as he makes small vocalizations while feeling his own arm he realizes his voice is high, like a little boy's... or like a girl's. He looks down at his chest, half hoping for, and half fearing that he'll see tits...
No boobs. But he's leaner. Still athletic, but with a slimmer build. He could pass for a muscular masculine girl or for a thin feminine guy. Either way, he thought he was hot. He was almost turned on, could feel it in his heart, but he notably felt nothing but flatness between his legs. It was weird that he didn't get a boner, and then weirder that he didn't feel his dick at all... 'Oh no' he thought.
Taking off his pajama pants, he realized he had nothing between his legs. No cock or balls, no pussy either. Just pubic hair and smooth skin. His mind still expects a penis to be there but there's nothing. He feels the place where his dick should be and it's just smooth, it's such an odd sensation, like something that just shouldn't be.
He's woken up as an entirely sexless being...