Anxiety in kids isn't always obvious, and will often look like misbehavior. A quick tip to ascertain if your child may be experiencing an anxious moment is to simply ask before disciplining. You can say something to the effect of, "I think you may be worried about something (or have a concern). What's going on?"
If we assume anxiety as the cause of problematic moments for kids, we are going to be correct a good percentage of the time.