Buffy answers that with a delighted smile and a kiss, because words (even the involuntarily blurted kind) fail her. Careless of her feet, she falls onto the bed and takes Spike with her.

...several hours later (the stamina has been mentioned) and she's resting her head on his shoulder, her long hair fanning out across his chest as she tries to catch her breath. "Wow," she says, very much inarticulately.