Imagine yourself being confused and baffled by something, and asking “Really?”. The intonation is rising, as is usual in questions. Imagine yourself hearing someone say something you are completely confident is absurdly false or a lie, and you want to suggest to the person that they’re wrong and you know the truth, by sarcastically asking “Really?”. The intonation is falling, closer to ordinary statements of fact.

OOP is using the full stop at the end of his “questons” to suggest the second, sarcastic intonation.