Regular adequate rest is mandatory to allow all body systems to rejuvenate and repair. Prolonged deprivation will result in cumulative negative effects. Adequate rest is particularly important while undergoing chiropractic manipulations or other corrective procedures.
A positive attitude and outlook will affect how much stress is internalized for your body to manage. Although you can't always control outside stressors such as the behaviour of others or other circumstances that affect you, you can control your attitude and how much you will allow stress to affect you.
It is important to control or manage the stresses you can, such as eating healthy, exercising, ensuring proper central nervous system functioning, and getting proper rest. For everything else, a good attitude is the best defense.