When a person sleeps, they are never completely unconscious of their surroundings. I suspect the same is true for people under anesthesia and as well as many coma patients.
I think much of this depends on how consciousness is defined and no clear distinction exists between conscious and unconscious. For example, consciousness can be defined as being aware of one's own sensations and surroundings. I can make an argument that plants are aware of light and shadows, day/night cycles, and gravity. Some plants have been shown to communicate with each other using odors. Plants also have immune systems. Immune systems need to be able to distinguish between harmful pathogens and the plants own cells.
I think a lot of people would say that a grasshopper has consciousness. If a grasshopper is conscious, then why not a box jellyfish? The box jellyfish might not have a brain, but it has sophisticated eyes with which it can use to see and actively chase after it's prey. Other jellyfish exhibit social behavior.