The 8th house is the house of death, the occult, and sudden, terrifying events. Rahu is the planet of fear, illusion, and extremes.
When Rahu sits in the 8th house, it gives the person an almost supernatural intuition for danger ("mushkil bhaap jata hai"). They can sense a crisis before it happens.
Dr. Rishi Rohit Sharma explains that this placement operates in absolute extremes. If Rahu is positive, this person becomes so powerful and intimidating that they make the whole world tremble ("duniya kampa deta hai"). But if Rahu is negative, they suffer from severe paranoia, phobias, and anxiety, constantly trembling in fear themselves ("khud kaamp jata hai").