Edgar Alan Poe once said, “I became insane, with long intervals of horrible sanity". This is also the fate which falls upon us in Sand is the Soul. In the game's narrative it's known as the Sand Curse - a direct consequence of being able to organically process the Sand. It gives the accursed the ability to defy death, but it greatly affects his consciousness and psyche, making him slowly descend into madness. The more times you need to get "resurrected", the greater the impact on your sanity.
Monstrous hallucinations, grotesque apparitions and gory visions await you at the end of the road when your body becomes more and more contaminated by the Sand. Moreover, the people around you are very much aware of your state. It can be recognized in your voice and gestures. That's why they will react to you differently depending on your sanity. The real question is, however, are they really there or is it only your delusion trying to make contact?
Not only do you need to worry about slowly spiraling into insanity, but addiction to the Sand seems to be a noteworthy issue. Think of the Sand as a kind of morphine. Use it too much and your body will be struck by side effects which, in case of Sand, manifest in the form of blurred and distorted vision. Thankfully, there is a drug which can soothe your high called the Boltons Remedy. Though you cannot heal your distorted mind, the calming agents may help you stay focused or at least, more stable.
Adding Sand is the Soul to your wishlist will help us stay more stable and focused. And it's mutually beneficial, as you'll be up to date with any important news and announcements regarding the game!