hello Mrs F and welcome
Yes aberwells puts it all very well. First, don't be scared - either of PD or posting here. There's a lot that can be done for PwP and their carers - and much of it is in this forum, and the rest is on this website.
Then, yes, 'fraid mood swings can be part of the package. i can argue black is white with my oh, and can be very curt. I mostly recognise it and can sometimes break the pattern.
If you have PD, it seems to me, you're a mixture of the PD and the meds you take, and you. Iif you have side effects from one drug, you may get relief with a different one . . . but it may not control your PD symptoms so well. and then there's you: as aberwells says, just having PD is enough to swing your mood.
So when he next talks to his specialist nurse or neuro, do mention the mood swings. They're important to the family. As i always say (oh god the cat's at it again) it's not your dad that has PD but the family, and you all need support with it.
hope this helps.
Best to both of you