People do not end up in wheelchairs just because they do not know where their feet are. Even those who wear AFO's and have no feeling in their feet. Some of those even drive which might be dicey unless they have hand controls. It doesn't have to be severe either before you don't know where your feet are. This condition is caused by many things - diseases or otherwise.

Proprioception: http://en.wikipedia.org/wiki/Proprioception

The ability to sense where your body parts are.

You don't know where parts of your body are especially in the dark. Police officers do sobriety checks like "walk the line". A good site.