There are many causes of arrhythmia, which can be physiological or pathological. Pathological causes can originate from the heart itself or from other diseases. For instance, normal individuals might experience sinus arrhythmia, and circumstances such as staying up late, emotional excitement, or excessive fatigue can lead to premature beats or sinus tachycardia, among others. Other diseases, such as hyperthyroidism or fever, can cause an increased heart rate. For example, pulmonary embolism can lead to atrial fibrillation. Heart-related diseases, like heart failure, can cause ventricular premature beats, and diseases of the sinoatrial node itself can lead to sick sinus syndrome, among others.