Being a patient/having a sick family member made me want to become a doctor. Many people are inspired to become a physician because they or a loved one have had personal experience with an illness or disability. If this is the case for you, then make sure you don't dwell on the sickness itself, don't overdramatize it, and don't lexpress it as your sole motivation.
Also, while it true that poignant tales of great emotional and personal struggle can provide strong evidence of your motivation for medical school, such a discussion must be handled with extreme sensitivity and care. Don't try to manipulate the reader's emotions or try to make them feel sorry for you.
Instead, focus on what about the experience of being sick or having a loved one being sick made you want to become a doctor. How did you grow as a person due to this experience? What did you learn from being a patient or having someone close to you being a patient with regard to the medical profession? What about the profession intrigues you? Do you know what goes into being a doctor? Have you observed a doctor for a long period of time? Do your research and show that you understand the life of a doctor and you have chosen it for a variety of reasons.