“Tonight I felt so incredibly lucky,” Rachel said to me in hushed tones as we laid in her double bed before falling asleep. It was the night of her 25th birthday, and we were tired after a day of flitting around New York and an evening of gorging on Italian food.

“I’m so glad!” I said. “We really wanted you to have a good birthday.” It had been months since I’d last seen Rachel. We’ve known each other since the second grade and have been close friends since college. But now we live in different cities and don’t see each other nearly enough.

In the weeks leading up to Rachel’s birthday, I had sensed that she wasn’t feeling like her usually chipper self. So last fall, I arranged to have two of her best friends from college, Lauren and Katie, travel down from New Hampshire to spend the weekend with us in New York. I took the Amtrak up from Washington, another close friend drove in from Philadelphia, and a smattering of New York-based friends joined us for dinner that Saturday night at Lil’ Frankie’s in the East Village.

After an evening of wine, pasta and burrata galore, a group of us boarded the R train to Astoria for a sleepover. The crew dispersed throughout Rachel’s railroad apartment, and I was lucky enough to sleep side-by-side with the birthday girl.

“I knew that Lauren and Katie were coming, and I was really excited about that,” Rachel gushed, “and then you came up from D.C., and that was so special, and then all those other people showed up at dinner. I just feel really loved.”

In my experience, shared sleeping quarters is where some of the best bonding and frankest conversations happen. There’s a magical intimacy that comes from talking to someone while the lights are off and you’re halfway to dreamland. It’s usually shared in the early stages of a romantic relationship, but one of the great benefits of being solo-ish is the access to platonic pillow talk.

Talking in the dark, there are no distractions. There are no facial cues to read, no expressions to decipher. You have to listen to each other’s breath, understand each other’s tone. Part of the intimacy comes from volume: You want your friend to hear every word you say, but you don’t want anyone else to. You also have a captive audience but are spared looking at the other person’s face and reading her reactions. You share your thoughts into a blank space, baby.

There’s a reason kids leave camp with best friends forever.

Some of my fondest childhood memories are of piling into Kate or Kristen’s bunk with my Girl Scout troop and chatting. Once the sun set and the chaperones retreated, barriers fell away.

At home, we were confined to the social order formed early in elementary school. The cool kids, the art aficionados, the soccer stars, we stuck with our sets. But late at night on those trips, whatever walls existed between us in the outside world toppled and we bonded over everything from our fears of being fat to our disdain for swimming in the cold lake and our worries about what the next school year would bring.

As adults, we don’t often have the chance to steal away to summer camp to let loose, learn archery and build friendships. Boy, are we missing out.

Hearing how our efforts had made Rachel feel made me so happy. I could hear her smiling as she talked about the evening, and that was 100 times better than seeing it. With the lights off, we spoke more slowly, more deliberately. When every word pierces silence you have to make them count.

After the birthday recapping, we talked about the guy I was dating at the time. He and I had just started getting into our own deep pillow talk, and it was nice to be able to dissect it in a similar setting.

“I recognize so much of myself in him. I think that’s why I feel so comfortable,” I confided. “Even the things that aren’t so great — like he told me he feels like he always has to project this sort of false outward persona — I get that, and that makes me want to be with him more.”

I hadn’t told those things to any other friends. I may not even have broached them with my therapist at that point. But in that darkened room in Astoria just a hand’s length away from a good friend, I let down my guard.

There’s a level of trust and comfort that Rachel and I share; you need that before you climb into bed with another person. Once you and your friend get to the point of “we accept that we may snore or pass gas or both,” it’s easy to imagine that they’ll accept anything you might say.

Before saying goodnight, Rachel said to me: “If you told me when I was 16 years old that I’d be lying in bed with Megan Downey on my 25th birthday, I wouldn’t have believed you.”

I wouldn’t have believed it either. But I’m so glad 16-year-old me would have been wrong.