Why do you think you're conscious in your own body as opposed to someone elses?

[DaveC426913]

...I think Descartes was right - if I'm not sure of the "I" existing then I will never be sure of anything. I believe "I" is real...

More to the point of what Descartes was trying to say: in order for there to be doubt about existence, there must be something doing the doubting. Labelling that something as "I" is a trivial last step.