in the torah (Bamidbar 5:21) it says that when the guilty Sotah drinks the water, her "belly will swell and her thigh will fall."
anyone have more details as to what this means. does it mean her leg falls off her body for example?
Note Rav Hirsch translates נֹפֶלֶת as "to waste" while Art Scroll translates it as to collapse. The chabad web site translates it as "rupture". This seems to be a sudden set of spasms that would cause the thigh muscles to collapse. The initial description seems to imply convulsions.
Rambam Hilchos Sotah Chapter three seems to say that her belly swells (as with gas or a major tumor) and the thigh ruptures, which seems to be the muscles of the thigh rupturing. Not that the translation seems to be "thigh" rather than the groin area and also that it seems to be something that is immediately obvious to the onlookers. Since the female groin area is "hidden" (unlike the usage with Avraham and Eliezer), it would seem to be the thigh and hip area muscles that rupture (as in a convulsion). However, this is my logic as I did not see explicit comments in the Rambam.
Halacha 16 says that the immediate effect is
her face will immediately turn pale yellow, her eyes will bulge forth, and her veins will surface.
This is so that she can immediately be removed from there
so that she does not have a menstrual emission [there], for women who are in a menstrual state make the Women's Courtyard impure.
 Sotah 20b states that the terror of death might provoke menstruation.
. The Rambam's wording, based on that of the Mishnah (Sotah 3:3), requires some clarification. The intent appears to be, not that the Women's Courtyard becomes impure, but that the woman becomes impure, and in that state she is forbidden to be in the Women's Courtyard. See Hilchot Bi'at HaMikdash 3:3.
He says in Halacha 17 that the same thing happens to the adulterer. This implies that the "belly" is not a euphemism for her womb but actually means the abdomen.