There is a wide range of conditions that can make it difficult for you to breathe while you sleep. These conditions are generally related to a heart or lung problem or to structural problems within the nasal passage. Sleep apnea is common among obese people and occurs when the airways becomes narrowed or floppy as you relax while you sleep. During sleep apnea you may stop breathing for periods of 10 seconds at a time, until your body realizes that your oxygen levels are low and wakes you up to breathe. Hypopnea is a similar condition to sleep apnea, but instead of having pauses in your breathing, you don't breathe properly, again causing oxygen levels in the blood to drop and waking you up. Trepopnea is when a person finds it difficult to breathe lying on one side. This usually occurs if a person has problem with one lung or bronchus or if they have heart failure.
If you feel short of breath whenever you lie down, you have a condition called orthopnea. Orthopnea is often caused by heart failure but also happens to people who have asthma or sleep apnea. Paroxysmal dyspnea, also known as cardiac asthma, is when you wake up suddenly after some hours of sleep and feel extremely short of breath, wheezy and have a cough. This resolves when you sit up. Cor pulmonale is a condition where the right side of the heart is not working properly, leading to high blood pressure and fluid build-up in the lungs. Cor pulmonale is caused when oxygen levels are constantly low due to a chronic lung disease, such as sleep apnea, chronic obstructive pulmonary disease, pulmonary hypertension and others. Pregnant women may have difficulty breathing due to the pressure of the baby on their chest when they lie down.