Nightmares

I propose adding nightmares that occur when a player hasn't slept for a long time (and is already being hunted by Phantoms) or when sleeping in uncomfortable conditions.

The concept is that the player might wake up from the nightmare; cave sounds could play, mob heads and armor stands might turn to face the sleeping player, and the "Seaside" painting could change to "Creebet."
Additionally, the player could be attacked by phantom versions of mobs—skeletons, zombies, or spiders—that appear to deal damage. If the player defeats them and goes back to sleep, they will wake up fully healed. If they don't go back to sleep, the night will skip automatically, and the player will be teleported to their bed with their health restored.

Even in Hardcore mode, if these mobs kill the player, they will immediately wake up in the same state they were in before the nightmare began.

A game rule should also be added to disable nightmares, just like the one for Phantoms.

Nightmare features could also include hearing various mob sounds from all directions or the sudden appearance of a screaming Enderman or Creeper. The player might even see themselves lying in the bed, hear chests and doors opening, or find themselves in a phantom world devoid of any entities.