Please explain what does it take to get sent to a mental hospital against your will?

Dangerousness: Each state in the us has laws specifying when someone can be "involuntarily committed." in the 1960s and 70s the states all adopted variations on a dangerousness standard, ie., suicidal or homicidal, plus in some states "grave disability", i.E, . Inability to provide food/clothing/shelter for oneself. Depending on the state, there is usually a review by a judge after a few days.