britney,
i second what randy wrote - sometimes there are emotions underneath that are just crying to get out. and sometimes an intense sexual interaction is the key that unlocks the floodgates [or in your case, faucet]. it's not usually the actual interaction that causes the tears of joy, but it triggers something else that causes the tears.
i've experienced a few non-playtime/hobby partners reacting this way, sometimes a little, sometimes a LOT of tears.
i've experienced only one or two playtime/hobby partners reacting this way, mostly just lasting 10-20 seconds.
i myself have cried a time or two after intense sexual interactions.
as with many emotional reactions, feel it, taste it, smell it, hear it, see it - experience it. DO NOT attempt to shut it down, deny it, bury it. to do so would be to deny/repress a part of you that is wanting to get out into the open. and that is generally not a emotionally healthy thing to do.
but, at the same time, do not obsess with it or over-analyze it. it's just a feeling that arose and is making itself known.
now, if this happens over and over and over, then it might be time to really look at it and explore what is going on in your life that might be causing these emotions.
oh, and btw, no charge. unless you want to cry on my shoulder for a bit after we engage in some intense deliteful sexual interactions.
and btw 2, i'll keep you in mind the next time i head to austin. do let us dallas guys know if you're thinking or planning a visit to our fair city.