Anesthesia lets us lose consciousness and then regain it. We're getting closer to knowing how general anesthesia works and the mystery of consciousness itself.
When someone goes under, their cognition and brain activity continue, but consciousness gets shut down. For example, it has been shown that rats can 'remember' odor experiences while under general anesthesia.
Anesthetics are fairly selective, subduing awareness while sparing non-conscious brain activity so the precise mechanism of anesthetic action should point to the mechanism for consciousness.