Nymphomania is very different from what I see described here. For a woman to be a
nymphomaniac, she must fit a couple of
conditions:
1) Engages in the act of sex COMPULSIVELY.
2) Does not derive pleasure from the sexual act.
Although having an "insatiable sexual appetite" is perfectly natural and healthy, being pathologically compelled to engage in sex joylessly is, in fact, a psychological disease. In true nymphomaniacs, the compulsion to engage in sexual activity overrides all other considerations, even though the afflicted individual does not actually enjoy the sexual act, and will not achieve orgasm.
To expound, individuals who enjoy having sex casually, or simply have a great sexual appetite are not, by definition, nymphomaniacs.
nymphomania can be caused by (among other things) childhood sexual abuse.
The male form of nymphomania is called "satyriasis".