Yes, I know all about PACs.
I don't know how effective diltiazem is, I don't take it. I'm put on beta blockers, that really helps treating PACs that occur with adrenaline. Calcium blockers like diltiazem and verapamil can be effective too, it's a bit trial and error, it all depends on what's causing them. If you have anxiety and somewhat elevated heart rate too, I guess beta blockers are best.
The best cure is, however, to accept PACs as the completely benign phenomenon it is. They won't cause any problems, they aren't more dangerous than an ordinary heartbeat, and though they can feel horrible (especially the "early" ones) they won't cause any harm. And they are NOT dangerous to the heart.
Easier said than done, of course. Keep in touch with your doctor and if the medication doesn't help, ask for beta blockers.
I've taken Diltiazem and it works quite well. I have PAC's, PVC's and PSVT (a type of atrial tachy). Years ago they gave me Verapamil (similar to Diltiazem) and it did not agree with me at all. I can't take beta blockers because I have asthma. But the Diltiazem helped with the chest pain, slowed down my heart rate and lower my BP a bit, helped with my Raynauds (where my blood vessels spasm and my hands and feet turn a yucky blue/gray color).
The only side effects I had from starting it was a little bit of fatigue and a whopper of a headache. The headache lasted a couple weeks then tapered off. It's all a vascular reaction to the med and once I got past that part, the medication was great. But each person is different.