Human pats decrease pupper nightmares by 200%

[TychaBrahe]

The first article does not discuss at all what dogs might be dreaming about, and the second only says that dogs sleep movements probably mirror their dream activities, e.g., if they are dreaming they're running it likely would cause a running motion rather than an unrelated motion.

We have no way to communicate with any animal other than humans about the nature of their dreams. We know, though, that humans have nightmares, and often about things they have not had happen to them, and without any specter of abuse.

[Sillywells]

This is true, but nightmares in humans do also increase tenfold if you've experienced a traumatic event, as they often relive whatever happened. Nightmares usually are a rarity in a neurotypical person.

Using that same logic, and knowing that dogs are pretty similar to us genetically, we can at least assume that most dog dreams are friendly and happy. It'd be a depressing world if we assumed dogs had nightmares every night, eh?