the Calling

There is a reason why no human can navigate through the mists of the Nydhira sea: they do not come back, and, in the rare occasions when one has been found and rescued by uiledath sailors, they are never the same again. They've heard the Calling of the Mists.
In Ashar, they say it's like having a foot in two worlds, and being in none. The people who've heard the Calling respond to things that no one else can see or hear. Sometimes they make no sense, but other times what they say has truth in it. They have visions of other worlds, or other times, creatures, or states of being. They also experience synaesthesia, even though sometimes the triggering stimuli are not experienced by anyone else. Their dreams are exceedingly vivid.
Most of the very few people who have heard the Calling cannot differentiate between what everyone experiences and what they alone experience. It becomes very difficult to communicate, because sometimes they think they speak, but they do not, and sometimes they speak when they didn't mean to. The more lucid, those who encountered the mists for a much shorter period of time, have tried to explain that there was a song, like many voices harmonising, and in it, through it, they were able to perceive ideas, emotions, and visions that they can neither escape nor replicate. They still experience those things, but they are better able to tell what is "real" and what is not.
The uiledath, who are wholly unaffected by the mists and navigate them without problems, call the Calling corcair, and perceive it as a colour that they've learnt to avoid. They claim that the corcair is what makes humans mad, even though they see it with their ears. Up till now, there are many theories and stories as to what causes the Calling, but no one really knows what it is in the mists that so profoundly affects humans.