Etimology
From Middle English yourself, equivalent to your + -self.
pronoun
yourself (referring to the person being spoken to, previously mentioned, the reflexive case of you)
(reflexive) Your own self (singular).
You (singular); used emphatically, especially to indicate exclusiveness of the referent's participation in the predicate, i.e., that no one else is involved.
Examples
Be careful with that fire or you'll burn yourself.
You yourself know that what you wrote was wrong.
After a good night's sleep you'll feel like yourself again.
I spoke with yourself last in February.