You don't actually get this achievement after the fight in Damascus because:
Rather, you fight Robert de Sable in a new area you can only get to from the kingdom. Once you get there you fight through a gauntlet of soldiers and Templars before finally reaching him.
The fight is two-fold. First you have to fight his Templars. Once you win, you can fight him. You unlock the achievement after the next couple scenes.
Also, disregard what Wayans said about the health bar. If you reach full sync before finishing each memory block, you'll get:
You don't actually need full heath at the end of every battle in order to get the achievement.