Perhaps you had a leak or even a exuberant drink bottle exploded, there are water stains on your ceiling. Rather than a whole new paint job, first try spritzing the stain with a mixture of 1/2 cup white vinegar and 2/3 cup of water. Lay an old sheet down on the floor while you are on the ladder. Let this sit overnight. Repeat in the morning if necessary. The vinegar will break down the hard water stains.