I have difficulty breathing when lying flat in bed but when i prop my head and shoulders it improves. why?

Concerning sign here: Shortness of breath with laying flat and improves with more upright position is a concerning symptom of heart failure, medically called orthopnea. Often fluid in the lungs settle at bottom with sitting, but spread upward with laying flat thus causing shortness of breath. Extreme obesity can also do this as pressure in belly pushes things up causing troubled breathing, ..Consult doc..Good luck.