Should you wake someone up while they are having a nightmare?

Well, it would probably be better for them, if they look like theyre not enjoying it? :O

Edit:

However, you are far more likely to remember a dream of any kind of you are awoken in the middle of it. Which is more important - saving someone from continuing their nightmare, or saving them from remembering it?

This isn't to say that if you leave them alone they won't remember it - they may wake up on their own, or if they sleep through it, they may still remember some of it in the morning. But they won't remember as much, and those memories are more likely to fade quickly.