Finally. My last character died due to me clicking on the floor too quickly and an elven tempest frying him to death.

@sprice2513: Did you install this addon after creating the character? Check the savefile description in the "Load game" dialog to see if it includes 'low_hp_popup' in the "Required addons" line. If not, there is a slightly hacky way to enable the addon for your current character if you're willing to perform minor savefile surgery. Otherwise, you'll just have to wait until your next character; We Apologize for the Inconvenience.™

I'm probably missing something, but where exactly do I activate this mod? After sucribing to it, and verifying it's in my mod list, I'm unable to locate it in the UI tab of the game options.