"Cognito ergo sum," or "I think therefore I am" was written by Decartes. Which is to say that the one thing one knows for real (even if there is a malevolent demon causing me to hallucinate reality) is that by thinking, is that because I think, I know I exist. Everything else might be a fiction, but my consciousness is not.
This is the foundation of the "am I conscious" question, and can be answered in this way. But is anyone else? Likely. It seems hard to believe that all other beings I interact with are merely *pretending* to be people. If they appear to think they are humans, and claim that they are conscious, than they likely are conscious beings. (Unless that malevolent demon is playing tricks again!)
But what about other animals? Chimpanzees can recognize themselves in a mirror. Does that mean they're conscious? (Perhaps conscious in a way that is different than us?) Dogs twitch in their sleep as though dreaming. Does that mean they have a rudimentary sense of consciousness? What about fish, who react to pain? (But may or may not dream. They certainly sleep, though!) Are they conscious?
It's an impossible question, because, ultimately, the only person I can answer the question of whether I am conscious or not for is myself. Everyone else is a guess, and a guess with less and less certainty as I look at creatures less and less like myself.
Yet it seems so important. Being conscious seems such a measure of who we are. If other people don't really experience the world, do they deserve our empathy? If fish are conscious, is it okay to eat them? What about plants? What about rocks? What about computers?
There's really no answer. But that's what makes the question so much fun!