I am intrigued by this question. Let me see if I can put my thoughts into words. Just breathing, or just being alive, would mean sleeping, eating, digesting, eliminating waste, and repeating that cycle. You could even throw in some form of passive entertainment, like watching TV. So, you'd wake around 10 AM, after sleeping for 12 hours, get up and have something to eat, watch TV, eat some more, watch more TV, eat some more, and finally go to bed. That is not living - that is just existing. To truly live, you would need to produce, create, contribute, etc. You would need to interact with your environment, learn, and grow. That would be the essence of it.
I am curious to see what others have to say.