Greetings and welcome to justanswer,
There are some common causes of such leg numbness.The common ones are nerve entrapment, nerve compression, diabetic neuropathy, stroke, spinal cord lession, etc.
The acue numbeness can be caused by the nerve compression commonly.Sometimes while sitting the compression on the nerves may cause such numbness sensation which may last for an hour or two.It will recover by itself with time and you need not worry.
The other possibility can be due to spinal cord lession or brain stroke which can also cause such sensation in you.The diabetes can also cuase such symptoms and you should check that also.
You should have the relevant investigations don elike ct scan brain, ct scan LS spine, x-ray ls spine, blood sugar, etc. after consulting your neurologist if your symptoms do not improve within a day or two to know the associated abnormality.
The treatment depends on the underlying cause.
Let me know if you have any doubt.