typically women dont naturally lose their sex drive until 45, so if your wife is around 30 the reasoning behind a loss of sex drive is usually emotional. it could either be thats just really stressed or might have depression.
usually with me, if it's been a stressful few months i have no desire for sex, and i do get even more upset when my fiance asks me about. usually when he just doesn't talk about it, and then he tries to get my mind of the stressful things in my life, it works.
o and i too can get wet when i dont want sex at all.
and i know when i say i'm tired, or i have to get up early, its just an excuse cause im not in the mood.