Twice in the past week my left foot from the ankle down turned ice cold to the touch & completely numb as i slept. what can it be?

Depends: You could be putting pressure on a nerve in your foot from the way you sleep but it can also mean there is some nerve impingement as high as your lower back. I suggest you see a Podiatrist first for an evaluation and a possible NCV (nerve conduction velocity) test of the lower extremity might be useful in determining your diagnosis.

An entrapped or: pinched nerve…could be coming from as high up as the lower back...