Get rid of the comma after inside a dream; this is an example of a sentence with a compound predicate (more than one verb with the same subject: You, in this case), which normally does not need a comma to separate the verbs. (Occasionally a comma is required for clarity, but don’t use one otherwise.)
Rather than change the em-dash after fact to a period and begin a new sentence (which would be correct, too), I changed the em-dash to a comma and added as before the second you.
Spell out numbers: five hundred, not 500. (Yes, it’s a number of years. No, that doesn’t mean it should be written with numerals the way you’d write a date.)
You are trapped inside a dream and fully aware of this fact, as you have been for the five hundred years you’ve been living here.