WOW, What a whopper!I don't know if my explanation will make much more sense than the dream itself. But here goes.
What you describe is kind of a plague-like illness,with many people dying.Illness usually means annoyance,in dreams.But Death,means the end of a cycle,something finally being over and done with-be it school(graduation is often seen as death),the end of a job,even finishing a term paper,if it's been a bitch to get done.
OK,you live upstairs in this dream.In most dreams,the house represents the "higher self",with each room representing an aspect of self,so to speak.In this case,though,you were in an upstairs apartment.Which could mean that we're talking about your own higher self,AND,your other self(aw,c'mon,we all have an other side,which likes to be mean).This other self is represented by the guy in diapers(with the diapers meaning your dirty little secrets-which we all have,as well).The diapers hung on the wall, are the secrets that you've shared,which are out there for all to see.
That the guy lunged at you isn't at all surprising,most of us fight with ourselves,over lots of different things.Sam protected the "higher" you,though,with a weapon.Which shows that you believe in him enough to come to your defense,even in your dreams.
I hope I made sense,and that some of this made some sense to you.