How does my brain come up with this shit?

The dream started normal enough then me and random people were leaving to get in a plane or something and these people had like 4 cats and 1 ran away up to like group of other cats and at first they were like o he's trying to fit in, then it was like "omg they're rejecting him" and the gang of cats like started ripping apart the one cat. I ran to try to save it and they tried to go after me and the poor cat was missing limbs and eyes. Shit was graphic

I slept quite well last night, night before though horrific nightmare woke up covered in sweat.
Like you say eff knows were your brain gets it from

I think that your sub-conscious tries to send a message through normal dreams but once it realised you don't remember it, it makes sure you remember it.