Your mind tries to take in the fractured reality of the planes but can't. Space folds into itself, and only madness and horror lies in the gaps that form. As you open your eyes, the madness just becomes more intense. The creature in front of you is ripping the remaining threats of sanity away. Their voice form in your head. Yes, it says, we will devour you first. As the mind-flayer steps closer, you hope being first will give your family a chance.
The most common theory is that aberrations originate from the Far Realm, but no one is sure. What is certain is that they warp the very fabric of reality around them. Some only in small ways, others for kilometres from where they live. Their influences on the mind can be staggering. In short, they will give you nightmares and then make those dreams reality.