When any planet receives bad aspects like square (90 deg) and opposition (180 deg).
When bad planets (Saturn, Mars, Rahu, Kethu, Uranus, Neptune, Pluto) are posited in bad houses like 6th house (place of disease), 8th house (place of longevity) and 12th house (place of death).
When bad planets occupy the signs: Virgo, Scorpio and Pisces.
When bad planets occupy the Ascendant (place of body, mind and soul).
Death can be predicted when Sun, Moon and Ascendant - all the three are afflicted.
The following are the characteristics given for houses/signs and planets, in connection to health of a person.
HOUSES AND SIGNS
Body in general, Head, Face, Facial bones, Brain and Blood Vessels of the brain, complexion.
Second house or Taurus:
Teeth, speech, right eye, Throat, Larynx, Cerebellum, Neck and Bones, Blood vessels and nerves connecting throat and neck.
Third house or Gemini:
Right ear, Shoulders, Collar, Hands and the related bones, Lungs, breath, blood.
Fourth house or Cancer:
Last phase of life, Chest, Breast, Ribs, Food poisoning, Stomach, Gastric and digestive system.
Fifth house or Leo:
Heart, mind, and Spinal chord.
Sixth house or Virgo:
Disease in general, Kidneys, Stomach, Bowels, Intestines and Abdomen.
Seventh house or Libra:
sp;Waist, Navel cavity, Lumbar region and skin.
Eighth house or Scorpio:
Incurable diseases, Urinary and sexual organs, Pelvic bones, Bladder, and anus.
Ninth house or Sagittarius:
Hips, Arterial system, Nerves and Thighs.
Tenth house or Capricorn:
Knees, Hams, Joints, and bones.
Eleventh house or Aquarius:
Legs, Blood circulation and ankles, Left ear.
Twelfth house or Pisces:
Lymphatic system, Feet and Toes, left eye, hospitalization, death.
Heart, Sun-stroke, Eyes, Blood circulation, Spinal cord, Right eye in males and left eye in females.
Cold, pneumonia, breast related diseases, kidneys, Stomach, and Uterus related problems, Mania, Motions, left eye in males, right eye in females.
Digestive system, nerves, Lungs, Speech related problems, Mouth, Tongue, Hands, Epilepsy.
Throat, neck, cheeks, skin, venereal diseases and reproductive organs.
Forehead, nose, muscles, male reproductive organs, piles, hemorrhage, injuries, burns, cuts, fevers, accidents, electric shock, suicidal tendencies.
Liver, diabetes, blood vessels, right ear, thigh, buttocks, obesity, problems due to excess-eating.
General weakness, bony appearance, Teeth, bones, knees, joints, rheumatism, chronic diseases, asthma, lungs-related diseases, tuberculosis and skin-related diseases.
Rahu is considered as equal to Saturn in Vedic Astrology. Rahu gives Leprosy, Cancer, diseases to spleen, poisoning, snake bite, bite of poisonous insects and creatures.
Kethu is considered as equal to Mars in Vedic Astrology. Kethu gives hypertensions, B.P., Lunacy, allergies and infectious diseases. When Kethu is involved, the real disease cannot be diagnosed by medical equipment.
Diseases to arteries, brain's nervous system, parts of spinal cord, electric shock, heart attack, sudden accidents and unknown diseases.
Psychic diseases, epilepsy, lunacy, food poisoning, drug addiction, conjunctivitis, drowning, delusions, insomnia, infectious and contagious diseases, bites of poisonous insects or animals.
Congenital diseases, venereal diseases and accidents, diseases due to harmful radiation like X-rays, atomic rays, UV rays, or radio-active rays.