In manga and anime, sometimes a character's eyes are drawn simplified as a single large X. This happens when the character's eyes are closed.
That is, this is a variation of >__<.
And it has nothing to do with X__X, which is when both eyes are drawn as x's.
Right: Honda Hanako 本田華子
Anime: Asobi Asobase あそびあそばせ (Episode 5)