I believe there to be a distinction between physically existing and the representational existing we conceive of in thought.
"For instance, how do I know I will still exist tomorrow?"
Well, isn't it only within our humanly embedded predicament that this thought exists? It seems rather ambiguous, the worry of continual existence, considered from a nonhuman entity (obviously).
It is a matter of representation from the physical unto the mental then, wherein this problem arises. I think it could be considered false, or of no meaning, that we may or may not exist tomorrow. I think it is a modified representation of reality that doesn't exist as a viable threat outside of our thought-oriented paradigm. Im aware this posits more questions than it answers, but I can't help but think of the question as meaningless.