As you may know, I seem to write a lot of crazy. And by "a lot" I obviously mean every other character...The list seems to include at least one character per chapter that's a little bit off their rocker. And, though it might not be obvious at first, you'll quickly see exactly what I mean.
Let's think... who are some of my special crazies?...
Elicith, Ero, Ve, Fes, Constantine, Drystan, Cassandra, Caps, Alasier, Maggie, Asper, and even Krys and Cadence are all various levels of mentally unstable.
So why? you may ask. Do you want the simple answer or the complicated one? Because the simple one is that aether affects the mind. A human mind can only handle so much aether at a time, overusing it, overdoing it, can cause a sort of psychosis, split personality disorder, or even drain your life.
You want complex?
Let's take the Dureri from my novella Adrianna. Obviously there's something unnatural about them, their actions seem to be outside the realm of normal human behavior. And yeah, sure, you can write that off as it being a simple matter of them not exactly being mortal in the strictest sense. But there's more to it. You can only torture people for so long without going just a little bit mad. Drystan is the best example of this.
In the first novella, Adrianna, the character of Drystan is explored a little. He's described as obsessive, clingy, and impulsive. He's described as hating who and what he is. At first glance this is brushed off with an explanation that may seem a little too easy: he views the body as sacred and doesn't like seeing anyone hurting - let alone doing the hurting himself. If you haven't read the book yet, please do so. Just keep in mind that this description of him isn't a cop out, I'm just holding out on you. ;)
Later in the series Drystan's psychosis deepens as he becomes more obsessed with Adrianna and goes down a... questionable path. I try to make it a little unclear as to why this is (after all, I have to keep challenging your mind, don't I?), however I will say this, being Dureri isn't all that it seems. Sure there's the glamor and the immortality and the inability to feel pain, but there's a little bit of a side affect that most Dureri don't even notice: split personality disorder. (This is explored in Adrianna, so if you have questions, go read the novella.)
The mind doesn't have the capability to deal with the whole new set of input, heightened senses, all the goodies of being Dureri. So, the mind creates a divergent personality that can cope with the entirely new life. Over time the two personality sets merge - usually as the trauma of being changed lessens - sometimes this creates a super genius like Renee, Gilgamesh or Nereida. And sometimes you get a messed up jumble of a person like in the cases of Cassandra and Drystan.
For other cases, you're just going to have to read through the stories, aren't you. ;)