So as it based on the show, when ever you ascend while in the abyss it will increase. I've recently added in tool tips for all traversing actions, so just hover over them, and it'll let you know how far vertically you travel, and then how much buildup you should expect.
Besides traversing, I want to add in things like running from fights, might cause you to run away upwards, etc.
At 100% you'll get a curse, for the first layer this will be just nausea. Layer 2 though will have minor body changes, and the lower you get, the more extreme.
If there's anything you think should be added in, or any curse ideas, be sure to let me know!