The learned Subramanyam has given a very comprehensive answer. I will just keep it simple.
Sickness, old age and death are the natural properties of all creation - you cannot avoid
sickness but you can change your attitude to sickness.
Morphine doesn’t stop the pain (which is always positive as the body is signaling that there
is a problem), it changes the way you think of the pain.
So when you are sick instead of lapsing into self-pity you should reflect on the suffering of
all sentient beings and think that there are so many millions that are suffering in worse ways
than you. Think of them, and wish that through your mental empathy with them, their
suffering should be decreased.
oṃ namo bhagavan vāsudeva dhanvantare,
mahā-viṣṇu nārāyaṇa vaikuṇṭa,
ārogyaṃ dehi dehi,
dirghāyuṣyaṃ dehi dehi,
śrī mūrtaye namas-svāhā ||
Salutations to the Lord Dhanvantari, the all-pervading Principle of Health,
The omnipresent one, the Ground of all Being, the un-impreded one.
Grant me health
Grant me long-life
Salutations to the manifestation of auspiciousness,
May my health and longevity be used for the welfare of all sentient beings.
Trayambakam Yajamahe, Sugandhim Pushti Vardhanam, Urvarukmiv Bandhanat,
Mrityurmokshaya Mamratat.
Some people feel it is chanted for getting a long life. But it’s a lifesaving Mantra. It can cure
any disease and should be chanted with sincerity, faith and devotion. Chant as many times
possible sitting next to people who are ill or under pain. Even a sick person can chant for
himself or herself. You can regularly chant or play it in a recorder if there is a terminally ill
patient around. If your friends or relatives are suffering from cancer, play the mantra or
chant regularly to reduce the pain. Chanting of Maha Mrityunjaya generates divine
vibrations that ward off all the negative and evil forces and creates a powerful protective
shield. Regular chanting will protect you from sudden death, accidents, famine, misfortunes
of any kind, calamity and unexplained situations. But don't chant mentally it should be
audible to you.
Have faith in Lord Shiva
Maha Mrityunjaya rejuvenates, bestows health, wealth, long life, peace, prosperity and
contentment.The healing and nourishing forces enter the human body through foods,
medicines, supportive emotions, and encouraging thoughts. The Maha Mrityunjaya Mantra
attracts these forces and creates an inner environment to enhance their effectiveness. Have
faith and Lord Shiva is there to protect you.
Namah Shivaya