Aneurysm.

This afternoon, my mood was suddenly and entirely altered, the way water reacts with deep, blue-black dye (which was, incidentally, part of the lab we were doing at the time).
I felt it swell inside of me, stretching the walls of my perfect cover frighteningly thin, and I almost burst. The tears and throbbing anguish would have drained out of me like hot arterial blood, pulsing scarlet, drowning the whole room, or worse, just me.
Fighting under the flawless surface without showing one ripple of discontent, I smiled weakly, became a little quieter, and held on until I could safely escape, betrayed only by the barely perceptible tremors in my fingers.

For once, I was glad to get away, glad that soon I would never have to come back.

If this is how the transition has to be, I'll take it gladly.
Anger and frustration are easier to deal with than longing.
Longing eats away at the lining of your heart and makes you shiver when it isn't cold.
It is treatable only with time, which just serves to increase the distance between you and what would make you whole. Gradually, you become accustomed to its absence, but the hole it leaves in you is never filled. It exists there forever, mocking your attempts to ignore it by flaring up in moments of vulnerability, choking you until you can get a hold on it again and push its head back under the surface.