It's not unusual for the feet to get a bit numb from long-duration riding, but the numbness wouldn't be expected to extend far from the contact point of the pedal.
The fact that the numbness extends up the leg suggests that it's neurological, likely due to a compressed nerve somewhere "upstream".
This can be a back problem, but may also be something akin to piriformis syndrome where the muscles of the upper leg compress nerves feeding down the leg. This is particularly likely if you've been hyper-exercising and are experiencing some degree of swelling of the upper leg muscles.
You need to cut back substantially in your training and see a doc. Kind of a toss-up as to whether it should be a neuro or an ortho -- I'd be slightly inclined towards the ortho, as he would be more familiar with disorders due to overtraining. Or a "sports medicine" guy might be good, if you can see one relatively quickly.
If the numbness progresses much, or if there is any accompanying paralysis, it would become a medical emergency.