Once you've become hidden, sneakng is the actual movement form that uyou would take. Page 252 of the Core reads, 'You're undetected by the creature during your movement and remain undetected by the creature at the end of it.'
You're undetected by the creature during your movement and remain undetected by the creature at the end of it.
Since you're still hidden 'at the end' of your movement, your target is stilstill flat-footed when uyou attack.