What happens if a lazy eye suddenly gets a lot worse?

Evaluate. A "lazy" is an eye that does not track with the other eye (in or out) due to poorer quality of vision from that eye in infancy and childhood. If there is a sudden worsening (turns in or out more) than the eye (s) need evaluation to see if there is an interior or muscular problem more than the initial event. You need to see your ophthalmologist for this.
See your doctor. Either it was poor for a while and you only recently had occasion to notice it, or something significant has occurred that should be evaluated.