I was in my acting class today and I thought about this question when our instructor was talking about various theories as to how to show emotion on stage.

Checkov came up with a theory (quite opposed to his teacher, who said that the key was to find emotional experiances in your own life that parallel the situation your character is going through and use that durring rehearsals to feel the emotion, and by the time you are in preformance it should come automaticlay with the situation on stage) that basicaly, if you can physicaly mimic certian aspects of the emotion you wish to portray it will help you to feel that emotion. Such as clenched fists when angry, scrunching your face up for crying, etc.

Anyway, as I thought about this (actualy it's an idea he covered in acting I also, this is II) I thought about your question and it came to me that maybe you are initiating a quasi-real crying session just by the act of shedding tears, and this is causing the emotional release.

I dunno, just an idea. I really don't know what I am talking about.