Water running out of a ceiling light fixture is an electrocution and structural collapse emergency. Water contacting energized fixtures creates a shock path to any surface it touches. Your first action is to cut power at the breaker serving that room — not just the light switch — before approaching the wet area.
Saturated drywall loses structural strength rapidly; a bulging or sagging ceiling can release all stored water and debris without warning. The water visible at the fixture is a fraction of total moisture present, since drywall, insulation, and plywood absorb significant water before releasing it. Without thermal imaging and moisture meters, hidden saturation cannot be found, and leftover moisture leads to mold growth within two weeks.
Exit any room with a sagging ceiling immediately and close the door. Shut off the water supply to the floor above if possible. Do not touch any wet electrical component.