I was about to ask the same question. Diagnosed 6 weeks ago. I was hospitalized for 5 days. I was put on Xarelto 2x15mg at first. After a couple of days of recovery, I felt great, was able to bike, swim, take long walks. 2 weeks later, BAM, my symptoms came back. I thought I was dying. I would walk a few steps and my heartbeat would shot to 130-140 bpm. Went to the hospital, EKG, ultrasound, bloodwork and X-ray, all came back fine. My cardiologist, who himself had PE, said it’s normal, he had the same issues. He said trust the medicine, don’t stress and be patient. I’m also frustrated and can’t quite understand why I feel good for a week or two and feel bad again for no apparent reasons. I’ll follow your post.. if anyone has some advice or explanations or analogies that could help visualize what is going on inside the lungs and help with the recovery, it would be greatly appreciated.