My dreams usually have a pattern to follow. When a dream is classified as a nightmare, it's a weird dream to me. This is due to the fact that I either dream about high school (yeah it finished ages ago and I still dream about it ugh), clouds (although this is becoming rarer now than it was in 2008), my birds escaping/dying/coming back to life, people online, spiders, Neighbours, frogs and sometimes Pokémon/AFL. If I have dreams that aren't about any of those really, it's weird.
An example that comes to my brain is when I dreamed about a dinosaur walking around the neighbourhood wanting to kill me. I sometimes dream of magical things occuring, such as a distant land, which is really my backyard - and then walking through portals to get to one side of the backyard to the other. I've also dreamed about people being really small and in pools, or giant blow up creatures that have no purpose in the dream whatsoever. Most of the time my dreams are based at my house, so it's meant to appear as if I'm at another place, but I'm in my house, so people having magical rituals in my backyard isn't exactly normal. Oh, another strange one was something about a man killing people because of something to do with their eyes about a year ago, I can't remember much about it now though.
In other words, I have weird dreams a lot but I try not to pay attention to them.