I'm new to Morrowind and I was sleeping outside of Molag Mar and it woke me up and this fish dude (argonian?) with one huge eye and one normal eye attacked me. I stabbed him like 50 times and he never died. I eventually died. Please explain this to me. I don't think its an assassin because he wasn't wearing robes or anything.

Well, he is an assassin, sent by the Dark Brotherhood to kill you. This is how the expansion "Tribunal" launches. Good luck for the future!

Are you using any mods? As far as I can remember, I was never attacked by any DB assassin that wasn't human [no Argonians or Khajiit]. Or could you have mistaken the DB armor for an Argonian's skin? http://www.uesp.net/wiki/File:TR-quest-Dark_Brotherhood_Attacks.jpg

No mods. I do have Tribunal because I got the GOTY version.

It normal then. The worst is that, if you belong to a faction, let's say the Mages Guild and you sleep inside the Mages guild building, you can be attacked there too, and nobody will ever lift a finger to help you...

I think he's confused. If you notice he says one big eye and one small eye, that's totally the dark brotherhood helmet.

OP, that was the dark brotherhood, he isn't wearing robes but actually light armour that's worth a decent amount if you can kill him. If you cant beat him yet, make sure you quicksave before sleeping until you kill one. Once you do kill one, go talk to a guard, and then the guard in ebonheart that they refer you to, and they shouldn't attack you anymore.

The assassin will take a little time to come down the hall to find you though, in the Mages's guild. It gives you a few seconds or so to get ready to fight.

Iirc, you can sleep in the bedroll in the room in the census office in Seyda Neen without getting attacked if you need time to level.

Not true, unfortunately. How many times have I been attacked there...