Wait... you... [She still doesn't have any answers, but she can see how upset he is. Willow says more strongly,] Karkat, stop. Tell me what's going on. There's a lot of-- of confusing interdimensional hijinks, okay, whatever you're thinking might not be true. Just calm down.

[She's already feeling the sting of irrational guilt at his distress, and it's going to get worse if she doesn't try to help him. She does want to make things better if she can-- she's just that compassionate-- but the guilt definitely spurs her along faster.]