What would cause my left foot to be numb and feel like it's sliding on ice when I walk? I've lost my balance and fallen twice.

That is a good reason to see an Orthopedic Dr.

I would see your GP first. (You haven't told us a single thing about you, which a doctor 'sees' when you walk in - gender, age, weight, then gets history and so on.)

The left leg is on the heart side, so circulation problems and high blood pressure are some of many MANY situations to consider.

I had similar sensations for many years, and it was treated successfully by a chiropractor, after getting nowhere with medical doctors. But I had pain starting high up on my abdomen, down my inner thigh, and my foot felt numb and freezing cold.

See a MD first.