Sometimes the bottom of your feet can become numb due to compression of the nerves in your feet.
In that case then the numbness in the bottom of your feet should go away on it's own within the day or a few hours.
Other causes of bottom of feet foot numbness are poor blood circulation, injury to the foot or other nerve damage to the foot.
Also if you're diabetic the diabetes can cause nerve damage which can cause the bottom of your feet and sometimes your whole feet to become numb and lose the feeling.
If you don't know you have diabetes and the bottom of your feet are constantly going numb then it would be a good idea to get checked out for diabetes or other conditions.