paroxysmal nocturnal dyspnea

n.
  1. Acute dyspnea caused by the lung congestion and edema that results from partial heart failure and occurring suddenly at night, usually an hour or two after the individual has fallen asleep.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.