I visit with my GI every 6 months (or sooner, if there's a problem).
Each time I visit him, he always asks, "Are you sweating at night?" He says he asks me this because sweating can be a sign of fever (it might just be a low-grade fever that doesn't even make you have that "feverish" feel) and a fever can be a sign of inflammation and inflammation can be a sign of active Crohn's.
That's the info I've been given on night-fevers.