Sleep, unmarred by illusions and fantasies... and if you can't dream, you don't have to worry about nightmares, right? Wrong. If you can't dream, your waking life becomes the nightmare. [...] Dreams, it seems, are needed to release the bad energies that accumulate in all of us... Without them, the mind tears itself to shreds in time.
Sahmad, Sahmad's Tale

The Dreaming Plague was a mental illness caused by Annona. It inhibited those infected from dreaming, and rendering them insane before they ultimately died. The plague was responsible for killing almost all the Iron Tribe members.

The plague was started by a being named Annona, an ancient creature living under the surface of Bara Magna which fed off the dreams of others. Starving for dreams, she eventually found the Iron Tribe and began to consume their dreams. After the process, the victim would be unable to dream, which would cause them to go insane and eventually die.

Many years later, around the time of the reformation of Spherus Magna, the plague began to affect Agori such as Metus again. Once Sahmad learned the plague had started again, he embarked on a quest to find whatever was responsible and destroy it. Eventually he, Metus, and Telluris encountered Annona on the surface world and, after a series of events, transported Annona to an unknown location and rid Bara Magna of the plague.