Things that used to bother my conscience do not register anymore. Honestly, that scares me more than the sin does.

“The heart is deceitful above all things, and desperately wicked: who can know it? I the LORD search the heart, I try the reins, even to give every man according to his ways, and according to the fruit of his doings.”

Jeremiah preached to a nation confident it was fine, right up until the collapse. His diagnosis is that the human heart is not a reliable narrator of itself, which is exactly why he says in the next breath that God searches it. The point is not that you are uniquely deceitful, but that self-examination alone has a ceiling. Someone outside your own head has to tell you where you are.

“Speaking lies in hypocrisy; having their conscience seared with a hot iron;”

Paul warns Timothy about teachers whose consciences have been cauterized, borrowing the image of skin burned until it stops feeling anything. It is not a description of monsters but of a process: repeated overrides of the same internal alarm until the alarm stops sounding. Notice that in your case the alarm is clearly still wired in, because the numbness is the thing frightening you.