How is the drug ketamine used?

It is used as a dissociative anaesthetic in surgery.

By this, it doesn't actually stop pain, so much as it "shifts" consciousness, allowing for a sort of disconnected state.

The same is said of out-of-body experiences, which are controlled by the same neurochemical mechanism.

It is able to do this by blocking (antagonizing) NMDA (N-methyl-D-aspartate) receptors used in glutaminergic neurotransmission.