I've encounter a bug during the quest "Under Saarthal", where I have to face against 3-4 draugh's, 1 of them has an infinite health, as I been blasting fire, slashing them, and other things. I don't know what cause this but the only way I could kill this and by using the console (i hope it won't cause me to lose my progress on earning achievement for using only that command against this bug). I don't know if this bug is rare to others but i will like to see this fix in the next future patch so I don't have to go trough this bug again.

Is there a big, big blue orb in the middle of the room?

Either activate it or shoot it with a spell.

No, that that room, it's after you got the speech with this "order" or something, and right after the circular room with 6 coffens and a bridge in the middle of the room where 3-4 normal leveled draugh and 1 restless draugh appears. one of the normal leveled one has unlimited health.

I just finished that quest about an hour ago it played fine here mate. Try reverting back to a previous save?