The causes of a sudden fluttering of the heart during sleep include physiological factors, cardiac arrhythmia, digestive diseases, respiratory diseases, and hyperthyroidism. 1. Physiological factors: when tiredness, late night will lead to increased nerve excitability, cardiac discomfort, there will be a feeling of heart shaking. 2. Cardiac arrhythmia: tachyarrhythmia, premature beats, conduction block, etc. may occur, and these diseases can cause symptoms of heart shaking. 3. Digestive system diseases: gastritis, gastric ulcer, gastroesophageal reflux can also cause discomfort in the precordial area. 4. Respiratory system diseases: pleurisy, intercostal neuritis, pleural effusion, etc. can manifest this chest tightness and palpitations. 5. Hyperthyroidism: Hyperthyroidism causes an increase in basal metabolic rate, leading to palpitations and panic. If sudden shaking of the heart is not relieved after resting, you should consult a doctor and take treatment according to the doctor’s advice.