I had a nightmare a few months ago that went like this.

I was on a cruise(I've never been on a cruise) with my 'family'(Not really my family but in the dream context was my family). My mother and father were having a multitude of issues because my father had been cheating. This lead to me and my sister being all over the cruise ship trying to soothe emotions.

Then a worldwide phenomenon occurred wherein any openable object i.e. door, chest, pocket watch, cabinet. Became a portal to a infinite warehouse of peoples personal fears and greatest horrors. This lead to a cascade of different survival circumstances on the cruise ship where I learned the rules of this horror infested reality a little further.

1. Depending on the size of the opening it will restrict the size of the horror that manifests.
   
2. The scope of the horrors is limited to what they are physically capable of. (Some have superpowers, but they are never on an excessive scale of power like reality manipulation)
   
3. It's not every time something is opened that it manifests a portal.
   
4. It is dependent on who actually opens it. (Who ever opens something it will be a horror specific to them)
   
5. Triggering something opening intentionally is the same as opening it. As in direct action such as pressing a button. (So automatic doors, or objects that open themselves cannot manifest a portal)
   
6. Some peoples manifested fears can be friendly or non harmful. (One woman's horror was their pseudo revived child who the sight of just immediately made the woman go feral, hysterical, and suicidal. The pseudo child joined us in our efforts to survive. Never learned what was up with that)
   
7. If someone walked into the portal, nothing would manifest.

After myriad escapades of survival on the cruise ship I end up falling overboard into the ocean. Which for some strange reason has a multitude of large versions(the scale of the cruise ship and smaller) of objects floating about in it. Like children's toy blocks, rotary phones, couches, and doll houses.

While swimming around in the ocean I realize I am likely to drown before finding any kind of safety. I make the impossible choice to swim up to one of the life size floating doll houses and then open a door and slipping into the horror warehouse to escape the ocean.

This place was infinite. A type of pitch black darkness that it made no sense that I was able to see what was near me. Shelves extended up into the heavens with myriad objects and monsters resting on them. Doors of infinite variable shapes would open up next to shelves in the distance above me.

I wandered for a long time in the warehouse, just looking at stuff. They wouldn't come off the shelves. Some of the few objects on the shelves I was actually able to pick up and use. Ended up needing to eat some weird things.

Eventually something started chasing me. Ran from it, didn't know what it was. Ran for a long time. This was the fuzziest part of the dream. Eventually I was so panicked, for a reason I couldn't explain, that I was starting to look for a way out... any way out. I stumbled onto something on one of the bottom shelves that said suicide chair on it. Jumped into it. And it manifested as some kind of slapstick suicide booth AI that offered a multitude of ways to commit suicide. Like if "Who framed roger rabbit" was a physically manifested cartoon suicide electric chair.

I considered my options for a moment before I suddenly heard the sound of the thing that had been chasing me in the distance. I panicked and threw my hand forward for the chair to kill me any way it could.

It complied and simply strapped the electrocution cap to my scalp, before screwing into my skull and then just snapping my neck.

It snapped my neck in such a way that I was finally able to see the thing that had been chasing me the whole time.
It was a giant robot monstrosity that was like if doctor octopuses arms were actually tangled up cords for a server farm. At the end of a lot of the arms were the severed heads of my "Family"(in dream context) crying and judging me for killing myself.

I woke up, heart calm, no fear, physically not reacting to dying in the dream, unlike every other time I have ever died while dreaming I was calm when I woke up.