When a man sees his deceased ancestors while he is comfortably seated or while he is lying in his bed, he turns mad. The spirit who causes this is called ancestral spirit.
आसीनश्च शयानश्च यः पश्यति नरः पितृन्। उन्माद्यति स तु क्षिप्रं स ज्ञेयस्तु पितृग्रहः॥