Ok that sounds pretty creepy...
is there anyway someone could have been hiding up there...
any history that you know of in that house??
was the items ie the xmas tree decorated with any thing strange or different, something that might give away the time period,


Perhaps
there was an alternative route into the attic? I suppose these items could have been placed by ghosts, but that would be EXTREMELY weird. How old do
you suppose those mattresses were? Either way, I don't know how someone could place objects of that size in your house without your knowledge.