Is it common for a narcissist to fabricate a whole story of how they went on vacation when in reality they hid at home?

YES Why? Because they don't value reality and truth as much as they value grandiOSity and admiration from others. They don't care if they have to lie about their entire life, if it makes them look good. They certainly won't have any problem lying about a "simple" vacation.

They are pathological liars. My ex N would make up entire stories of his life while in reality he did nothing but sit home, drink etc. He made his life out to be some fabulous thing when he had nothing but have a crappy one. It's common.