Hello there

Well I don't know about crying during sex but there are quite a few women who cry after sex, particularly after orgasm.  I think this is far more common than we know.  

When you think about it, sex can be such an emotional experience with hormones rising and falling.  It is also a release both physically and emotionally. 

In this forum there is a discussion of this phemomena of crying after sex which goes on for eight pages!  So it seems it is an experience that more than a few people have.

And In this Associated Content article, Steve Thompson answers the question of why some women cry after sex.

When you started to cry was it after orgasm?  Is there any possibility that you were feeling sick because you describe things as feeling a bit altered.  Were you experiencing pain at all? 

I wouldn't worry too much about it but do see if this happens again.  Perhaps this is something you could discuss with your doctor if you are concerned.