It was not so much that My Lovely Wife got what’s called an undercut haircut — a style favored by “the youth” that features a partly shaved cranium — or that she dyed the resultant stubble on the right half of her head purple. It’s that she didn’t tell me about it beforehand, leaving me to discover her rather alarming new do at a barbecue we were attending.

As hamburgers sizzled on the grill, Ruth tilted her head to the side and the long hair she’d brushed over her undercut fell away, revealing that periwinkle fuzz.

That this happened in a dream and not in real life did not lessen the shock.

I woke up in a snit — Couldn’t you at least have warned me? — and spent the morning angry at my wife. At breakfast, I seethed silently.

I couldn’t say, “Don’t tell me you don’t know what you did.” She didn’t know what she did. Also: She didn’t do it.

Scientists don’t actually know why humans experience sleep mentation, a fancy name for dreaming. On his dreamresearch.net website, researcher G. William Domhoff of the University of California at Santa Cruz notes that dreaming is most likely “the accidental by-product of the coincidental intersection of adequate brain activation and the brain’s ‘Default Network,’ ” that is, the part of the brain that is active during passive moments.

So: Dreaming is an accident. (Kind of like Ruth’s haircut! Har-har.) Even though dreams don’t mean anything, that doesn’t, um, mean that humans don’t assign meaning to them.

As Domhoff writes, we have “developed ‘uses’ for our dreams as part of our cultural lore. Looking at them in the light of waking day, and believing that they may be full of insight, we may sometimes come up with new ideas or insights while studying them.”

But what if the insight is: I’m inexplicably mad at my partner? Is that fair?

“I remember pretty clearly my college girlfriend would get mad at me for things I did to her in her dreams,” said Dylan Faulkner Selterman, a senior lecturer in the Department of Psychology at the University of Maryland. “A lot of people have anecdotally reported feeling and experiencing this.”

Selterman set out to explore this phenomenon. The result was a paper published in 2014 in the journal Social Psychological and Personality Science. The title: “Dreaming of You: Behavior and Emotion in Dreams of Significant Others Predict Subsequent Relational Behavior.”

Selterman and his collaborators recruited 61 college undergraduates, collecting the 842 dreams their subjects dreamed over a two-week period. More than 85 percent of the participants dreamed about their partners.

“I didn’t know I was going to see so many dreams that involved infidelity,” Selterman said. “I wasn’t expecting that.”

I’m not interested in the infidelity dreams — or the sex dreams, and there were plenty of those. I’m interested in the “conflict” dreams and what happened the next day.

And what happened? When people dreamed about conflict, jealousy or betrayal, they had more conflict with their partners after waking up from those dreams. Selterman said the study marked the first time specific dream content had been shown to predict subsequent behavior with relationship partners.

This could be an example of what psychologists call “priming.” The dream produces a domino effect that helps turn conflict in a dream into conflict in reality.

“I think it’s not necessarily the case that any type of dream content would influence people’s behavior,” Selterman told me. “We found evidence that specific relationship content influenced that relationship.”

So, I’m not alone. It has gotten to the point where when I look at My Lovely Wife funny in the morning, she says, “What did I do this time?”

I worry that she’ll think my subconscious is doing the talking and my dreams reveal what I really think about her. But I can’t be held responsible for my dreams, can I? Not if she shouldn’t be held responsible for what she does in my dreams.

Selterman has moved on to a different area of research, one inspired by reports that the coronavirus pandemic has caused people to dream funny. Since the spring of 2020, he has been collecting dreams to see what, if anything, is going on. (To participate, go to dylanselterman.com/pandemic-dreams.html.)

After I’ve had a conflict dream about Ruth, my bad mood is usually gone by lunch and I’m able to laugh about it.

Selterman says there is no grand, unified theory of dreams but notes, “Our dreams are doing something. It’s beyond the meaning that we draw from them.”

The meaning we ascribe to a dream depends on a lot of things, chiefly, I suppose, how seriously we take our dreams. I think of my dreams as entertainment, though they are occasionally useful. (I’ve gotten column ideas from dreams.)

Have you ever acted upon a dream? Did you dream a winning lottery number or solve a pesky work problem? Did a dream inspire you to do something you’re glad you did — or wish you hadn’t done? Send the specifics — with “Dream On” in the subject line — to me at john.kelly@washpost.com.

Sleep tight.

Twitter: @johnkelly

For previous columns, visit washingtonpost.com/john-kelly.