And this from Wikipedia:
                                       La petite mort (French pronunciation: ?[la p?tit m??], the little death) is an expression which means "the brief loss or weakening of consciousness" and in modern usage refers specifically to "the sensation of orgasm as likened to death."[1]

The first attested use of the expression in English was in 1572 with the meaning of "fainting fit." It later came to mean "nervous spasm" as well. The first attested use with the meaning of "orgasm" was only in 1882.[1] In modern usage, this term has generally been interpreted to describe the post-orgasmic state of unconsciousness that some people have after having some sexual experiences.

More widely, it can refer to the spiritual release that comes with orgasm or to a short period of melancholy or transcendence as a result of the expenditure of the "life force." Literary critic Roland Barthes spoke of la petite mort as the chief objective of reading literature, the feeling one should get when experiencing any great literature.

The term "la petite mort" does not always apply to sexual experiences. It can also be used when some undesired thing has happened to a person and has affected them so much that "a part of them dies inside." A literary example of this is found in Thomas Hardy's Tess of the D'Urbervilles when he uses the phrase to describe how Tess feels after she comes across a particularly gruesome omen after meeting with her own rapist:

"She felt the petite mort at this unexpectedly gruesome information, and left the solitary man behind her."