You stop existing.
A quibble. How are you defining existence? How are you defining "you"?
If I suffer a heart attack right now and "die," as in, my heart and brain cease to function, my body still exists, but my perception does not. So, if you're speaking of "you" being "your perception," then, in an existential way, you're right, but only from the point of view of the deceased. If another existentialist comes trotting along, it's not as if the deceased's lack of self-awareness prevents the living from tripping over the corpus.