Lying on the side with chest tightness and shortness of breath dyspnea may be physiological reasons, but also may be caused by heart disease, lung disease, chest disease and other factors. 1. Physiological reasons: some people due to recent stress, mental tension, there may be chest tightness, shortness of breath, dyspnea and other discomforts, generally in the emotional calming, can be improved after rest, usually no special discomfort. 2. Heart disease: when lying on the side due to body position, can lead to increase the return blood flow, if originally accompanied by the left heart insufficiency and lung stasis, the increase in return blood flow can lead to lung stasis aggravated, then cause chest tightness, shortness of breath and dyspnea symptoms. 3. Lung diseases: people suffering from chronic obstructive pulmonary disease, emphysema and other lung diseases, when lying on the side due to diaphragmatic activity compression of lung tissue, which can have an impact on pulmonary ventilation and gas exchange function, which leads to symptoms of chest tightness, shortness of breath and dyspnea. 4. Thoracic diseases: when there are pleurisy and pleural effusion and other thoracic diseases, the diaphragm can move upward when lying on the side, affecting pulmonary ventilation and air exchange, resulting in chest tightness, shortness of breath and dyspnea and other symptoms. Side lying chest tightness shortness of breath dyspnea may also be seen in other diseases, it is recommended to consult a doctor in time, under the guidance of specialists to actively carry out the appropriate treatment, which will help to alleviate the uncomfortable symptoms as soon as possible.