Morphine can make you feel sleepy, dizzy, faint, or very relaxed. It can increase the chance of falling. Walking, getting up, and changing positions can be risky when taking morphine because it can cause lightheadedness, drowsiness, and cause you to be unsteady. Morphine affects the central nervous system. Morphine is used to treat moderate to severe pain and comes in a liquid form or tablets. It is an opioid pain reliever that binds to opioid receptors in the brain.