If I am sick, will meditation help cure me? Can I meditate if I am in poor health?
It can help, but it is a far better prevention than a cure. As the nervous system becomes more balanced over time from a regular routine of daily meditation, the body's immune system functions much more efficiently, and there is far less chance of falling sick.
Advanced yoga practices in general enhance the body's resistance to illness. Balance and purity of body and mind are known to be among the best defenses against disease. Meditation and other methods of yoga are important contributors. You could say that good health is a coincident benefit of long-term meditation practice, a foundation upon which we are building a much greater thing - enlightenment.