How hard could It be to take a plunge in a winter sea?

Or, When does a bracing dip become hypothermia?

Holly Nadler, left, and Ana Petrakova run into the surf. —Stacey Rupolo

This is something that apparently only a handful of oddballs EVER want to do. Oh, sure, there are scattered people all over the world who swear by the health benefits of submersing their bodies in water cold enough to flash-freeze flaming marshmallows, but the way I found out that no one cared to try this enterprise was the following: Whenever I mentioned that I and my courageous young friend, Ana Petrakova, 33, of Farm Hill Road in West Tisbury, intended to take a freezing plunge in Vineyard Sound in March, and then I followed it up with, “Would you care to join us?” each and every presumptive candidate said “No.” Just “No.”

So why was I doing it, the cold swim? Frankly, I felt the same intuitive dread of all the naysayers. Dread that it would hurt like hell. Also, sting, paralyze, and did I mention, trigger a heart attack.

But … here’s the thing. Ana’s mom, Timi Brown, 57, also a dear friend, and Ana, mentioned to me that during that warm snap we’d enjoyed a few weeks ago, the two nutjobs skedaddled down to Inkwell Beach in Oak Bluffs, stripped their clothes down to bathing suits, and paddled around in the water.

Back at home, I Googled “health benefits of cold-water dips,” and oh, daddy! once you educate yourself in all the advantages, not only do you want to belly-flop into a frozen fjord, you realize that if everyone took freezing-cold plunges, we could dismantle the whole unholy healthcare system, like, tomorrow!

First, it gives you energy to click up your heels and sing “Zip-a-Dee-Doo-Dah.” It helps asthma. It spikes up your antioxidant levels, provides a 40 percent drop in respiratory infections, makes you athletic, youthful, and toned, activates the immune system and, here the girls-only stuff — flushes impurities, improves the complexion, and stops cellulite in its hideous tracks.

But here’s what hooked me: It puts a zing in your mood. I’ve always had less of a zing and more of a ding in my moods. I’m probably, in doctorspeak, a bit unipolar, meaning that on the manic-depressive spectrum (which we’re all on; it’s the human condition), my lows are lowish, although not SO low that they’re anywhere near Virginia Woolf’s lows, but my highs are on the level of, “Oh, Halley’s Comet is coming back? I’ll have to check my calendar.”

But the fact is, you receive an uplift from cold water. In fact, here’s how one of the websites puts it: It’s a “feeling of well-being so encompassing, it becomes addictive.” What it boils down to is that the fight-or-flight shock of the chill releases those sublime endorphins, dopamine and serotonin: organic opiates.

So let us fast-forward to this past Monday, March 20, just for the record the first day of spring, which felt like anything but. Still, the forecast showed still frostier days to come, so we thought we — that is, Ana and I; Timi was working — would choose this relatively balmy weather of sunny skies and mid-40s temperatures. We even played with our odds through the hourly report: Whereas 1 pm was showing up at 39°, 3 pm promised to be a scorching 4° warmer!

About a block from the shore, I could see choppy waves with streaming white froth jetting back behind them. It was the kind of sight which normally makes me think, “Turn back toward town, babe.”

But, no, I had an appointment with young Stacey Rupolo, staff photographer for the paper, and Ana. Stacey was there first, snugged up against the part of the jetty that runs up on the sand, protecting herself from a bitter wind.

Stacey’s first words to me as I stood before her in two layers of leggings, a long-sleeved shirt, a white sweater thick as a Belgian waffle, High Sierra winter boots, a wool cap, and gloves, were, “Did you bring a towel?”

Huh. A towel. What a concept.

As soon as Ana arrived, we worked on our drill: We’d take off our layers lickety-split, piling them in the order in which we’d prefer to don them again. It wasn’t an encouraging start, in that the minute our boots came off, the sand under our bare feet was numbingly cold. If we couldn’t take this … well, no time to think about it. In the harshly windy Not Ready for Springtime air, we yanked off our apparel and, on the count of one-two-the-heck-with-it-GO! we charged toward the water, shrieking and hollering all the way.

At the water’s edge, my feet froze like swordfish chunks on dry ice. I kept running with my eyes on Ana ahead of me, who suddenly went down. I did as much of a dive as you can achieve in 14 inches of water, stayed submerged for half a sec, then stood, pivoted, and fled for shore.

As we emerged from 39° water, the air temp of 45° felt downright balmy. We scrambled back into our clothes with the haste of cartoon characters. I don’t know if this aftereffect came from traumatic amnesia, but my immediate recollection of the whole thing was utter exhilaration, zero pain. “Wasn’t that amazing!” I kept saying.

Back at my apartment, we sipped hot chocolate, then parted ways with a bear hug like survivors of the Donner party. I’m now writing this on the following morning, and I still feel ab fab. I hope the euphoria lasts a full six or seven days. I don’t fancy taking frigid dunks like that more than once a week.