I was barefoot cleaning my garbage disposal. one hand touching water and the other hand accidentally touched an exposed (metal) light switch for the disposal and it was on. i felt a humming feeling through my left arm and burning.. am i okay???

I think you will be OK from the electrical exposure from the medical standpoint. You may want to have an electrician check the light switch and disposal to be sure they are set up and grounded properly.

Electrical shocks, like lightning strikes, cause maximal injury immediately, and delayed reactions are distinctly unusual. It appears that your event was minor, and based on your post, see no reason for worry. Contact your local doctor if you do not feel well or have problems with your left arm.