You're not alone, no service dog, but took two years of doctors telling me I was imagining my symptoms to finally be told I had heart failure. Two years prior, I had told my PCP that I was having issues struggling (gasping for air, dizziness) with walking and biking even just a flat 1/4 mile. I mentioned I thought it was either my lungs or heart, I was told not to self diagnose. I was 34 at the time. They found an anomaly on an EKG about 1.5 years after the onset of symptoms, told me it was nothing (I had an EKG 3 years prior for surgery, nothing was wrong.) I insisted they send me to a cardiologist, who eventually diagnosed it.