košmar

1. nightmare
   Cele noći sam sanjao košmare. — I had nightmares all night.
   Probudila se iz košmara sva u znoju. — She woke up from a nightmare covered in sweat.
2. nightmare; chaos
   Vožnja kroz grad u špicu je pravi košmar. — Driving through town at rush hour is a real nightmare.
   U glavi mi je potpuni košmar. — My head is in complete chaos.

For a bad dream, noćna mora is just as common.