Is attic mold dangerous?

Attic sheathing mold is common here and it is a building problem first. If the hatch is closed and the insulation is dry, it is not automatically circulating through your bedroom. It still means moisture is hitting the roof deck, which can rot wood and, if insulation gets wet, become a smell and a spore source.

Do not live in the attic and do not scrub the deck without footing and protection. Have it looked at, clean what is colonized, and fix the fan, the ice dam, or the leak that fed it.