I'm no expert, but I do know that a woman's hormones are very strongly tied to serotonin, the neurotransmitter that, among other things, is tied to pleasure. It could be that you are experiencing a dip in serotonin (which would make you want to cry or make you lose interest) because of low testosterone levels or high estrogen levels (the two seem to follow each other anyway).

A question I would have, is have you tried the old way you used to do it recently? It could also be that you are conditioned to the easy orgasm from the foot method you use. I know that when I can't get myself off it aggravates me =/

I'm really not an expert on any of this and a woman would be a lot more help. Anyone else have a similar experience?