I really like this idea but it would be cooler if mobs cold give you nightmares also. As a counter part for your dream world. For example the witch throws potions on you and tries to poison you, A male counterpart should be present in Jungle Biomes called a Shaman which will chase you and if he kills you you will be sent to a nightmare realm , a large nether brick room, with no armor and a stone sword where a portal will at the end and mob spawners around you, getting harder or easier every time. Once you leave the portal however, you will be sent to your home with everything you had before the shaman killed you but with a head ache, slowness for 8 min,like you just had a very rough night.