When an Arisen's Sekhem shows through to the mortal world, it can overwhelm any humans unlucky enough to witness it. Called "the Sickness" this condition can either be a source of general unease or a stark terror when the mummy's Sekhem flares. The terror Sybaris can be triggered by outsiders witnessing the mummy returning to Descent, undergoing resurrection, spending a level of Sekhem, or revealing its corpse-like khat. Reactions to these things are similar to Lunacy when humans see an Uratha in unnatural forms or Bedlam from the magic of changelings: those weak of will might run in blind terror or go into a catatonic fugue state while others could grovel before the Arisen or lash out with sudden violence.
The unease Sybaris is not a momentary thing but more of an aura that surrounds the mummy, making it more like a Promethean's Disquiet. A human might feel the unease Sybaris when meeting a mummy (or its Sadikh) face-to-face, entering its tomb, or spending a day near a mummy. Unease is calculated by subtracting a mummy's Sekhem rating from its Memory; the lowest (negative) unease ratings flood mortals nearby with visions of the Underworld while the highest ratings have little or no effect on them.
After experiencing the Sickness (in either form) a mortal might have lingering visions from what he saw. After thinking on his experience for six hours or so, a mortal can make a Composure + Occult roll to understand a Sybaritic omen from the visions. Arisen cannot see omens in this way from their own Sekhem but they can get the information out of mortals who have felt the Sickness.