Premonitions are basically feelings towards something that's about to happen. I mean, everything you read on the internet, has to be true! That was complete and total sarcasm. It's common to see things in your dreams and they come true. It happens, but it's not something you need to worry about. Nothing is set in stone. Even if your mind comes up with this wickedly vivid dream, the future always changes, so it doesn't always come true.
I've had incidences to where I know I'll forget little things. Like my laptop charger or a pencil, or my keys. That's premonition, and your gut feeling that something is going to happen. And normally I do forget little things like that, haha. Deja vu is also common. It's fascinating to experience it, and it often happens to me. But it's nothing to lose sleep over, either.