About 5 days ago, the skin on the upper left side of my left foot went numb. no diabetes, good blood pressure, not sure what's causing it. ?

Nerve issus: Numbness is caused by some nerve issue. See your Dr to start and maybe even a Podiatrist if your symptoms persist, as you would then need to be evaluated for a nerve issue. Good luck.

A nerve problem: can be divided into sick nerves and compressed nerves. You can then look at the distribution (one tiny, tiny area). Sick nerves go from the ends backward; they are due to overall processes like diabetes and as such hit more than one area typically. TIGHT SHOES cause temporary numbness in a small area. This is a typical distribution for HIGH HEELS. cannot say in your particular case, but generally,

Numb foot: I am glad that you thought of diabetes, as neuropathy, resulting in numbness of the feet, is common in diabetics. In the absence of trauma or a skin lesion, it is hard to say without seeing it. Perhaps you have been wearing tight shoes which temporarily affected your sensation. I do not think it is serious, but if it persists, see your doctor.