Nocturnal angina is usually more likely to occur in the prone angina. Recumbent angina, which occurs at rest or during sleep, often in the middle of the night and occasionally at midnight, is not easily relieved by nitroglycerin and may be associated with dreams, lowered blood pressure at night or unrecognized left heart failure resulting in narrowed coronary arteries and inadequate blood supply to the distal myocardium, or may be caused by increased venous return flow when lying down, increased cardiac workload and oxygen demand, which can easily lead to myocardial infarction or sudden death.