Every so often my left ear will go numb and my hearing in that ear will fade. It's been doing this for a long time, but usually goes back to normal after a few seconds. My most recent problem is that it's lasting for more than five minutes and during that time my ear has no feeling. And hearing-wise it's like having a hand cupped over my ear blocking out sound. Can anyone give me a clue about this?

I am not a doctor. It looks like you may have a slight case of eustachian tube dysfunction. The eustachian tube suddenly closes, causing a negative pressure in the middle ear. This causes a numb, blocked feeling and loss of hearing. Since it has gotten worse, see your doctor and ask for a referral to an ENT or otologist. They can tell if it is serious or not.