I had a moment like that once, only it was the exact opposite. I realized that I cared deeply for and about everyone and everything around me, and I stopped denying that that part of me existed, the eight-year-old that would weep over any suffering, regardless of how small or inane, that I tried to stomp out years ago because I knew that to live that way would be to hurt every day. I went right on hurting and feeling the same things, of course, knowing all the pain in the world, but ignoring them. Then this past summer I got sick of it... Realized in an instant that I had been lying to everyone around me, and how could I blame them for having misconceptions when I was the one fueling them, and turned around and accepted the way I am. Now I'm even going all in and majoring in psychology purely so that I can help others, probably specifically either children, prisoners, or addicts (haven't decided lulz, but I identify with all of them for personal reasons), when previously I would have been like, "LOL Y R U SUGGESTIN THAT," while secretly wanting it all along.
I told my closest three friends all of this in much more detail, and they know who I am. Everybody else still makes inaccurate comments, but it's OK; I rather like that protection, that mask. It gets annoying and old at times, but really... I don't like people to see me, beyond a superficial level. When someone makes a stupid remark that isn't really true, I'll say, "I care...." but that's all. That's basically all I've said in this post, too. lol.
For a while there, though, I had almost fooled myself into thinking that I cared so very little.

This post was so tl;dr as usual.