Unconscious: This is the most common and direct opposite. It refers to a state of being unaware or not responsive to the environment.
Subconscious: This refers to mental processes that occur below the level of conscious awareness. It's not entirely the opposite, as it still relates to the mind, but it emphasizes the hidden or automatic aspects.
Inconscious: This is a less common alternative to "unconscious," but it carries the same meaning.
Nonconscious: This emphasizes the lack of awareness and distinguishes it from subconscious processes.
Insentient: This refers to the lack of feeling or sensation, implying a complete absence of consciousness.
Unknowing: This emphasizes the lack of knowledge or awareness.
Unwitting: This implies that something is done without conscious awareness or intention.
The best opposite for "conscious" will depend on the specific context and the intended meaning.