Heart Failure: Early Signs and Symptoms

I can’t sleep lying down or even with a slight angle. Shortly after attempting to sleep, I wake up with lungs seemingly filled with fluid; feels like I’m drowning. When I’m upright, lungs are clear, and the doctor hears nothing. I’ve had x-rays, CT scan, and nothing shows, yet I must try and sleep sitting up. I’m exhausted. I don’t know what to do. I am worried this may be a symptom of biventricular heart failure.