Apnea

Everyone dreams in REM sleep. But we remember those dreams best when we wake up before it ends. Living out a dream to the very end means we are more likely to forget it.

Charlotte tells Gale that no matter what, that dream will be with him, even if he remembers not.

Gale is like Dawn, except forgetting his night dreams.
(Dawn is aimless for she has forgotten her dreams, her purpose in life.)