Suddenly Ill, help

I took my kids out for a fun day on Saturday and not long after getting home and being exhausted, I had horrible body aches, my heart was racing, my head felt foggy and I was freezing, like could not get warm. It pretty much hasn’t gone away. It came on so sudden. I went to the er specifically because my heart was racing and I have a heart condition. They gave me fluids and did an ekg and blood work. My d-dimer came back slightly elevated so I had a ct scan for pulmonary embolism but that came back fine. I truly have no idea where this extremely sudden Illness came from. Can someone give me ideas?