Bad Dreams v Nightmares

I couldn't tell you the last time I had a nightmare. Of course, now that I've said that, I'm probably going to have a wicked horrible one tonight, but that's besides the point.
Bad dreams on the other hand.... Well, before Sunday night, I couldn't have told you the last time I had one. Since Sunday though, I've been plagued by them. One (at least one) every time I fall asleep for a good time.
Now, you may be asking: What's the difference between a bad dream and nightmare?
I don't know if there's a universal definition, but a nightmare, to me, is when some scary mass murdered is after you or when someone you love dearly passes away. I still remember my first nightmare, and it involved skeletons chasing me with knives. Weird... And scary.
A bad dream on the other hand... Things just aren't right in a bad dream - -They're not how they're suppose to be. People are saying "I love you" to the wrong people. Kissing people who they aren't meant to be with. Things just aren't how they're meant to be in real life. Vague, but those kinds of things. Now, I couldn't tell you the first bad dream I ever had... Maybe my puppy ran away or something, but lately... They've been bugging me. And I know, I know, they're just dreams, right? But then I think about all the deja vu that I've had throughout my years and how it always results in a flashback to some dream that I had. And that isn't in the least bit comforting.