In order for you to make a valid Will you must have, in the eyes of the law, the mental capacity to do so. This means that you must understand and be able to decide what you are doing. You must be able to choose for yourself what you want your Will to contain. If you have a medical condition that could call into question your ability to make decisions about what you should include in your Will you should ask your doctor to certify that you are capable of making a Will.