Waking up gasping for air at night can be a symptom of heart failure — when your heart cannot pump enough oxygen-rich blood to meet your body's needs. Blood that flows too slowly backs up in your vessels. Fluid then leaks out of those vessels and collects in your body's tissues. When fluid builds up in and around your lungs, breathing becomes harder. Lying flat can make this worse. Most heart failure symptoms come from reduced blood flow and fluid buildup. Talk to your care team about what you are experiencing.