Hot water tap gone from dripping to gushing without me turning?

Hi, the hot water tap on the wash basin was dripping very slightly for some time. I had the washer replaced when I had my bathroom tiled, but it didn't seem to help. The tap has just started (at 2am) gushing while I was asleep in bed (so not turned the tap at all). I have turned the water off at the stop tap, but not sure how to proceed now. Any ideas please?