I consider myself to have a higher sex drive than what's normal, especially for a woman. As far as being addicted to sex, I never thought about it seriously. But I did google sex addiction when you posted this as I didn't want to give an ignorant reply, and I can't deny that I fit the bill for a sex addict.

I don't know if it's common in NPD, but I do know that promiscuous behavior is pretty common in BPD and ASPD and that symptom can certainly be a symptom of sex addiction.

I have personal experiences having been in a relationship with a narcissist that indicate they can certainly have issues in the bedroom.

I'll wait for our resident "classic" narcissist to chime in here. I don't know everything.