Orthopnea is a medical term which means, a condition associated with asthma and certain heart problems in which one can breath satisfactorily in erect position i.e sitting straight or standing only. They cannot sleep comfortably by just lying down normally.
People having such problems find more comfortable when they use more than 2/3 pillows under their head to ease breathing.
Doctor to Nurse: Place more pillows under the head of the orthopnea patient.
My co-passenger was suffering from orthopnea and I let her have my pillow also to make her sleep comfortably.