http://dom3.servegame.com/wiki/Affliction for more on afflictions. If somebody also wants to write a more in depth page about immortals (it is currently only on the abilities page, and it is a bit short). Go ahead!
This just sparked a thought that I don't have time to test at the moment:
Immortality works like healing.
Afflictions on units with old age don't heal normally.
in an odd statistical twist, my immortal got killed 3 times in one battle, and racked up 5 afflictions. he healed none for two turns, then 4 on the third turn.