Apathy is a horrible state to be in.
Great music affecting you the same as white noise, becoming something that you process in a corner of your brain without feeling any emotions.
Wonderful works of literature not filling you with that rush, a heady mix of anticipation, thrill and amazement generated by a few scratches on a piece of paper. Instead not even being able to recollect the last word that you read before switching to a new tab. Not feeling it worth the effort to open a book. Feeling nothing reading the Charge of the Rohirrim. Reading trashy novels to blame the book than yourself over not feeling anything.
Avoiding interactions because it makes you feel less. Your life feeling empty and colourless and the sparks and glitters of other lives blind you and exposing your shortcomings, imagined or not. Talking to people and conversations becoming something that last the duration of the interaction. Promptly forgetting it instead of reminiscing, revelling in or even getting angry about it later. Forgetting, sometimes deliberately and mostly out of reflex to talk to people important to you because you want them to see you at your best.
Being lonely in a crowd with the flip of a switch. Feeling conflicted due to the crowd inside your head telling you too many contrasting things that you end up ignoring instead.
Screwing up your life in different ways and hiding away from the world in a corner of your room. Getting anxious even thinking about trying to fix things because it is sure to go wrong.
Not realizing all this is happening to you till others point it out and then promptly ignoring it.
Apathy is a horrible state to be in