Try some back stretches and also strengthen your core to help improve and stabilize the muscles/spine. It's highly likely prolonged duration of sitting or standing can cause weakness in the muscles and one of your vertebrae are weak and easily loosened....can pinch or irritate the spinal cord or other nerves.
Which toes or part of the foot/feet do you feel the most pins and needles sensations?
Where did you fall and mess up your back...where on the back exactly and where if there is, any pain on your back?
Next, try to see if it matches the specific dermatome: here
In most situations involving the foot, vertebrae L4-S1 are usually related. But to figure out which vertebrae you have to figure out what part of the foot and where on your back did you fall/injure. Sometimes, pain location or irritation or discomfort isn't the root or source of the problem. In your case, there may be nothing wrong at all with your toes/feet (other than standing too much with excessive weight).
Some stretches here and here.
The most simple way to increase strength in the lower back is to do squats, just like here. Other exercises.