When you experience numbness that occurs in both your feet and ankles it can be caused by a pinched nerve which can sometimes and should go away on it's own unless the pinched nerve is completely damaged.
If the numbness in your feet and ankles doesn't go away within 1 or 2 days or constantly comes back you should speak with a doctor about it.
Sometimes foot numbness can be a sign of diabetes but usually the diabetes only causes foot numbness but it can sometimes cause ankles to become numb to to bad nerves.
Foot numbness is not always dangerous or a sign of anything bad and sometimes your feet can become numb just because the blood flow has become restricted or you have pinched a nerve in your foot.
However if the foot numbness continues constantly then it can be a sign of diabetes or Peripheral neuropathy which is caused by damage to your peripheral nerves.
If the foot numbness continues or comes back often then I would tell a doctor about the foot numbness so they can make sure it's nothing more serious.
But sometimes the foot numbness especially if it constantly happens can be a sign of diabetes because foot numbness does sometimes occur with diabetes.