Morrowind:Sleepers Awake

Summary
This quest is different from normal quests in some aspects. There are multiple separate events that start and update the quest and there are different ways to solve it.

While advancing through the Main Quest, various events will occur that show the growing influence of the Sixth House. Several people will start talking oddly, announcing the rise of Dagoth Ur, and you will receive a couple of disturbing dreams and cultists will eventually attack you in your sleep.

The events that trigger this quest will start during Caius Cosades' first quest. The quest will remain active during the entire Main Quest, and be marked as finished after destroying Dagoth Ur.

Events
Disturbing Dreams
 

While advancing through the informant quests given by Caius Cosades and sleeping in Ald'ruhn, Balmora or Vivec you will receive disturbing dreams about a tall figure with a golden mask (Dagoth Ur). You will receive your first dream after you have returned the Dwemer Puzzle Box during the Antabolis Informant quest, your second and third after you talk with Addhiranirr and Mehra Milo, respectively, during the Vivec Informants quest. You will receive the last dream after the Zainsubani Informant quest.

After having the first dream, you can talk about it with a few people by mentioning the disturbing dreams topic. Caius Cosades will be worried, but can only warn you not to listen to them. Mehra Milo will advise you to speak to an Ashlander about this. If you talk to an Ashlander they will just direct you to a Wise Woman, though Hassour Zainsubani can tell you a bit more about them. Of all the Wise Women, Nibani Maesa of the Urshilaku Camp, will be best able to explain the dreams to you. This will not stop the dreams from occurring though.

Sleepers Awake
After you have returned the Dwemer Puzzle Box during the Antabolis Informant quest, you will notice various Dark Elves approaching you at night. They will speak oddly about the rise of Dagoth Ur and call themselves "Sleepers". If you are a Dark Elf, they will invite you to come to the Red Mountain and join the Sixth House. If you are not, they will warn you to leave Morrowind while you still can. Each time they speak to you, their disposition towards you will drop. Be careful: If they hate you enough, they might attack you.

The Sleepers are:
Alvura Othrenim, in the Arena Waistworks in Vivec
Eralane Hledas, in the St. Olms Canal North-One in Vivec
Nelmil Hler, in the Redoran Waistworks in Vivec
Relur Faryon, in the Hlaalu Canalworks In Vivec
Vivyne Andrano, in the St. Delyn Waistworks in Vivec
Dralas Gilu, in Pelagiad
Llandras Belaal, in Balmora
Rararyn Radarys, in Balmora
Assi Serimilk, in Maar Gan
Daynasa Telandas, on the Arano Plantation
Drarayne Girith, in the Plot and Plaster in Tel Aruhn
Dravasa Andrethi's, in his house in Ald'ruhn
Endris Dilmyn, in his shack in Khuul
Neldris Llervu, in Suran
Vireveri Darethran, in Ald Velothi

Attacked by Cultists
After you have completed the Sixth House Base quest, and sleep in Ald'ruhn, Balmora or Vivec you will be attacked by an ash zombie. You can report this to Caius Cosades and he will advise you to sleep outside of town. He will also advise you to search for a nearby base of Sixth House cultists before they attack you again.

Breaking the Curse
There is one definitive way to solve the quest, and that is to destroy Dagoth Ur. This will stop the attacks and will lift the spell that was influencing the Sleepers.

It is also possible to stop these events by killing the four cultists responsible: Dagoth Fovon, Dagoth Hlevul, Hanarai Assutlanipal, and Dagoth Draven. All four cultists can be killed at any time, despite any quests associated with them.

Dagoth Hlevul in Assemanu
The House Hlaalu quest Control the Ordinators involves retrieving an artifact in Assemanu. Dagoth Hlevul can be found in Assemanu, Shrine.

Killing Dagoth Hlevul will save Alvura Othrenim, Eralane Hledas, Nelmil Hler, Relur Faryon, Vivyne Andrano, Daynasa Telandas and Neldris Llervu from Dagoth Ur's influence, and stop the attacks when sleeping in Vivec.

Dagoth Fovon in Hassour
The Tribunal Temple quest Dark Cult in Hassour sends you to Hassour to eliminate the Sixth House cult there, and ultimately Dagoth Fovon.

Killing Dagoth Fovon will save Dralas Gilu, Drarayne Girith, Llandras Belaal and Rararyn Radarys from Dagoth Ur's influence, and stop the attacks when sleeping in Balmora.

Hanarai Assutlanipal in Ald'ruhn
The House Redoran quest Ash Statue deals with tracking down Hanarai Assutlanipal, the cultist in Ald'ruhn. She can be found in her own house. The most likely way to stumble across her is through rumors about Morvayn Manor having been trashed by monsters, and decide to do a little investigating on your own account - which will give you the ash statue, and may open up the subject of ash statues with others such as Lloros Sarano, Varvur Sarethi and Galtis Guvron, who becomes hostile at the subject and drops a note that mentions her first name.

Killing Hanarai Assutlanipal will save Dravasa Andrethi from Dagoth Ur's influence, and stop the attacks when sleeping in Ald'ruhn.

Dagoth Draven in Subdun
Dagoth Draven is not involved in any quests. He can be found in Subdun, Shrine. Subdun is located on a rocky island off the northwest coast of Morrowind (the nearest landmarks are Koal Cave and Berandas).

Killing Dagoth Draven will save Assi Serimilk, Endris Dilmyn and Vireveri Darethran from Dagoth Ur's influence.

Reaping the Rewards
No-one will give you a reward when completing this quest, but after you have saved a Sleeper from Dagoth Ur's influence, by either finishing the Main Quest or killing the cultist responsible, you can talk to him or her. They will thank you for saving them and state that they will tell everyone they know how you saved them, causing you to gain 1 Reputation point. This can be done with every Sleeper for a total of 15 Reputation points.

Notes
The quest will still remain active after eliminating the four cultists. Completing The Citadels of the Sixth House quest will remove it from the journal.
If you are attacked by a cultist in a certain town, you will not be attacked there again until you have slept at least once outside that town.
If you kill an essential NPC (with the exception of Vivec), sleepers will refuse to speak to you and cannot be cured, even after completing the Main Quest.

Bugs
 
 

Quest Stages