Many possibilities. Numbness can occur from various reasons. Some potential causes include vitamin deficiency, nerve damage, nerve compression, and alcohol over consumption, side effects of different medications, or as a result of different systemic medical conditions such as diabetes. Get evaluated by a professional to determine the diagnosis. Treatment is based on the diagnosis.
A number of things. They can include tight fitting stockings and/or shoes, overuse, neuropathy from diabetes or other medical reasons, a local nerve issue such as a neuroma or tarsal tunnel syndrome, radiculopathy- nerve issues in the low back or leg (such as sciatica) that refer pain down. I would suggest that if it persists more than a couple of days and/or gets worse, to seek a podiatrist.