As far as the mechanic of FD itself: perhaps in classic it followed a simple rule, but by Kunark it should follow something similar to what is seen in this post:
http://www.eqmacwiki.com/w/Guide_to_Feign_Death
Standing Up
When you stand up after a feign death, if the previously aggro'd mobs were below Level 35 there will be no repercussions as the mob will have no recollection of you and carry on as normal. Mobs above Level 35 however have a chance to re agro on you. If they do, they will go directly to you as if you were still an enemy. If you have stayed down long enough for the mob to return to its spawn point, then there is a 90% chance it wont agro on you again. However, if it is still roaming there is an 80% chance that it will agro on you again. Don't be too worried though, you do have the chance to re-feign and each subsequent feign reduces the chances of re-agro by roughly 20%.
This rule is not universal however. Certain factors can influence it and different mobs will react in different ways. Distances from the mob when you stand up can affect its chance of re-aggroing, and some mobs will forget every time but will remember if you get close in the future. A way around this is to /quit while feigning death. This causes you to go link dead, but keeps you feigned, and so after three minutes you will time out as if you had camped and will lose all mob agro. However, before you do this you should make sure you are in an area with no mobs around, this will stop others from aggroing on you as you will log back in standing.