No one can say for certain what it was without a read out of your heart but it is possible for pacs to come in bigeminy. It is very possible the stress from your dream elevated your heart rate and any form of bigeminy felt faster. It is possible you had some runs of pacs or pvcs. That said, if you weren't feeling faint or short of breath or having chest pains it was likely nothing to be too concerned over. Again, more likely a response to the adrenaline from the stress of the dream. Try not to worry too much about it. Take care.
You possibly seem to misunderstand something.
Bigeminy (especially the ventricular variant) is usually experienced as a sudden reduction of your heart rate to half, with very hard beats (the ones you feel). Occational skips are "normal" PACs or PVCs, which in fact bigeminy also is, just that the arrhythmia occur in a pattern, not randomly.
What you describe is very common and may have several causes. Often, when the heart rate is slow, the premature beat (atrial or ventricular) will not prevent the next normal beat from occurring. This is known as interpolated premature beats, and may origin both from atria and ventricles. If this rhythm goes into a bigeminy pattern, you may experience it as doubled heart rate (as you have two pacemakers firing like ping pong but usually it's no system in this, you may get an occational beat squeezed in between the normal beats. This extra beat may also occur in a couplet, but if so, the heart rate must be fairly slow.
Atrial bigeminy is definitely possible, as you asked.
Try to relax, reduce the stress. Palpitations are common after nightmares. See your doctor if you get worse or anything changes.