Tunat will select a random LP to heal him (you can tell by the spell effects on them when he emotes.) If you kill this LP before it heals Tunat, he will not get healed and the LP casts Spiritual Wake on death. (On the raid)
[Sat Aug 01 23:42:42 2015] You gained raid experience!
[Sat Aug 01 23:42:42 2015] The phylactery crumbles to the ground, releasing the energy stored within it.
[Sat Aug 01 23:42:42 2015] You crush Living Phylactery for 74981 points of damage.
[Sat Aug 01 23:42:42 2015] You have slain Living Phylactery!
[Sat Aug 01 23:42:42 2015] You harvest energy from your slain opponent.
[Sat Aug 01 23:42:42 2015] Living Phylactery tries to hit YOU, but YOU riposte!
[Sat Aug 01 23:42:42 2015] Living Phylactery begins to cast a spell. <Spiritual Wake>
[Sat Aug 01 23:42:42 2015] You are rejuvenated. You have been healed for 10000 points.
Unsure if the AEs are related to Tunat selecting that LP to heal him, but I didn't always see them casting them.