One needs to be practicing vigilance in order to control his mind or should I say, to prevent his mind from controling him.
Life always gives you challenges and it’s sometimes easy to get emotionally caught up (change your mood).
Mood swings are not desirable for PD.
By being vigilant of what is going on in your mind, you can prevent mood swings from happening.
If they happen after all, just get a grip over yourself, take a few conscious breaths and start all over. Next time you will be more alert.