Early treatment of mental illness involved because doctors believed that doing this would drain the mental illness out of the person’s body.

not entirely certain but a possible answer could be "trephination"

Explanation:

people used to cut holes in people's heads to relieve them from mental illness. also called skull drilling.

depression is an ongoing sadness\lack of motivation. you feel and feel like its never going to get better. you're so sad to the point you think of death.

anxiety is an ongoing feeling of paranoia\ feeling like everyone is watching you and making fun of you. you get nervous easily and feel like the room is spinning.  

yes, they cause death every year. its a long, exhausting battle. only few make it through as sad as it sounds.

explanation: