Pulmonary embolism.

Question: A healthy 26 year old male, who has never had any health complaints before in his life, suddenly experiences an episode in which he is unable to breathe properly. He soon begins to regularly experience painful cramps in his feet. He becomes prone to sensations of breathlessness. He develops restless leg syndrome. He frequently feels short of breath. These symptoms all progressively happen more and more frequently, and last for longer periods of time each time they occur. Six years later, the male is now 31 years old, and now experiences all these symptoms every day. He now also suffers from constant fatigue, and he struggles to process and retain information. His feet always feel cold, even when the rest of his body feels hot. Sometimes his heart beats so strongly that the metal frame of his bed squeaks in time with his pulse, but his heart rate doesn't go up. He becomes physically exhausted doing simple tasks like washing the dishes. Before all these symptoms began, he was very physically active and was able to go for hour-long runs every evening, and do a hundred push-ups every day. Since these symptoms began however, he can barely stand up for too long without becoming physically exhausted. He had an MRI performed when he was 27 years old but the doctors found nothing unusual in his results. He had an x-ray taken of his lungs but the doctors found nothing unusual. He has had multiple blood tests conducted over the years but the doctors have found nothing unusual. He has had an echocardiogram performed but the doctors found nothing unusual. His illness is not psychological in nature. What condition could be causing these symptoms that the doctors have not yet been able to detect?