Could someone explain SK FD mechanics to me.

[Dumesh Uhl'Belk]

Apart from the fact that it has a cast time, it is no different.

The length of time you stay down has no relation to whether or not mobs remember you. The FD for 3 min to wipe aggro was added later... except that by staying down longer, you give mobs a chance to wander back to their spawn point (which guarantees aggro wipe). If you get up before they return to their spawn points, something like 98% chance to reaggro. There are a few tricks to bypass this. Play around with your hide skill and the circlet of shadows to learn more.