Asthma can be graded as mild, moderate or severe. Patients with mild asthma only feel shortness of breath when walking, but they can breathe normally or lie down and rest without any major impact on their lives. Patients with moderate asthma experience shortness of breath when talking and have difficulty breathing when resting flat on their back, but are more comfortable when sitting or standing. Patients with severe asthma have a greater impact on their lives and may experience dyspnea while sleeping and resting, and are unable to speak at a faster rate, usually speaking only single words.