I've had my feet go numb a few times when I was working.
It seemed to be when I tied my shoes too tightly over the instep.
If you have a high instep, there is an alternate way to ties shoes to keep pressure off the nerves in the top of the foot.
That website is very good to evaluate pain and foot discomforts.
They have nice anatomical diagrams showing where the nerves are in the foot, too.
I get numbness also when my blood sugar is low. When my thyroid was not working well, I had mega numbness in my hands too. But that kind of numbness was all the time, and not episodic.
One thing that may help if you suspect low blood sugar is to take some acetyl carnitine an hour before workouts. It helps burn fatty acids when the glucose gets too low...the mitochondria switch over and keep the energy going. It can also help with lactic acid build up from exercise.