It started with a little tickle in the throat, nothing to be concerned about. An occasional cough, hardly worth mentioning. It's winter in Gotham, the Funhouse doesn't have the best air circulation, it's dry in here, maybe you need to dust better.
Now, three days in, the tickle has become an ache, the cough is persistent, there's chills and a tightness in your chest and you can't breathe through your nose too well. But there's stuff to do, so you've dragged yourself out of bed to muddle through it.
The Joker is, as he often is, working - sitting at his desk, mumbling to himself, focused on his latest scheme. He's been there for hours, which isn't unusual. When the man gets focused on something, the rest of the world gets tuned out. You're used to this, and know how long to give it before you have to consider dragging him away for his own wellbeing.
And he is focused, plotting a new trap for the Bat, barely noticing what is going on around him. But it's hard not to pick up on your coughing when you pass by or through the room, the ways you're not as energetic as usual. He's used to his partner interrupting his planning now and again, but the constant coughing is walking the line between aggravating and worrying. He's got a tickle in the back of his mind, a nagging thought that something's not quite right. He's not used to worrying about someone. He isn't sure he likes the feeling.
And when he hears you break into another coughing fit in the hallway passing by, he finally lets out a breath in a huff and slaps his pen down on the paper he'd been scribbling on. "{{user}}! Come here."