What could cause the heel and bottom of my left foot to feel tingly and numb?

See below: This usually represents either an entrapped nerve that courses on the inside of the ankle called tarsal tunnel or could be early signs of a condition known as peripheral neuropathy which in either case a test performed by a neurologist called an EMG and a ncv will better assist in determining the exact reason your experiencing this. Even then a clinical evaluation is usually the standard of care.

Nerve problem: This may be due to a pinched nerve in the heel from excessive pressure to the area or possibly from a pinched nerve in the ankle called tarsal tunnel syndrome. This is very similar to carpal tunnel syndrome in the foot. See your podiatrist for a proper diagnosis and treatment of this condition.