The unexpected e-mail arrived shortly after lunch last Thursday. “Keep Drinkin’,” instructed the cryptic title, followed by just as strange a message:

“Well, as I figure it, you should be about halfway through that gallon of ‘gunk.’ Just keep on drinkin’.”

What the heck? Ah, yes. I had told our church blood-drive organizer I’d be “otherwise disposed” with a colonoscopy the day she wanted me to donate blood. Thursday was “preparation day” — when you drink a gallon of the “flush you out” stuff so the scopey thing gets a clear view of your down-under innards. My blood-drive friend remembered my anxiety and was pitching in with e-mail encouragement as I struggled to guzzle the flusher goop over the next two hours.

It’s not that the stuff tastes so bad. It’s just that a gallon of anything in two hours — save beer — is nearly enough to choke on. But with a little help from my friend, I drank it all up and flushed it all down.

I wrote her back: “You reckon pretty close to straight. All drunk up. Oh boy.”

“Look at it this way,” she replied, ”You get a real nice nap tomorrow morning.” She’s right. Nowadays, they use some pretty comforting drugs. You just don’t care what’s happening back there.

“But this part doesn’t feel so good,” I e-mailed back, completely bloated with a gallon of the salty, strange lemon-lime solution.

“But,” she countered, “You feel so good when it is over. You are really clean clear through.”

“My insides are baptized,” I quipped.

At 3:30 p.m., I’m praying to lose the gallon of goo sloshing around my guts. It’s just a matter of waiting around until, ahem, things flush out. Eventually, the magic juice does its job, and I’m going with the flow and feeling better.

The big hitch for the rest of the day is no eating anything, save yellow or green Jell-O and chicken broth. I’m haunted and taunted with images of cheese and salami slices. Can’t get ’em out of my head.

“You don’t know what you’ve got til it’s gone,” they say, and I’ll never take eating savory foods for granted again. Let’s save Jell-O for desert. While it may provide a clear view for colonoscopies, Jell-O is no satisfying main course.

Well, the gig is up at 8 a.m. Friday morning. Before my wife Carrie and I leave for my appointment, I check my e-mail one last time.

My friend had posted one last humorous poke: “Just wanted to tell you we hope everything comes out OK. You can take that however you want. Hank said that he prayed for you this morning and has your backside covered.”

Glad Hank had my backside covered, because once I put on my hospital gown, no one else did. No one likes those gowns except staff who must be forever giggling behind our backs. My gown was super loose, open and had a little blue diamond pattern that made it look more like grandma’s old muumuu than a serious medical garment.

I suggested to my nurse that patients would be much more cooperative and much less shamed if gowns were themed with NASCAR or NBA images for the guys, and perhaps Victoria’s Secret pink or Chanel for the women.

“Nothing doing,” she vetoed, adding with hospital authority. “Open your gown and lay on the bed with your butt fully exposed to the bed.” Today would be all about being open. There’s not much modesty with a colonoscopy.

Once we finally got into it, the good drugs I’d heard about kicked in and I faded long before I had any chance to provide further unsolicited helpful advice. I woke up with my wife and doctor by my side, saying everything looked good, save one little polyp to be sent to the lab. “No problems, everything looks normal.”

Well that’s good and reassuring. Through this whole process I learned that regular five-year interval colonoscopies after 50 are the single-most effective treatment to avoid cancer. So man up — or girl up — take the scope and you get a 50-percent improvement on avoiding colon cancer. Not a bad trade for 24 hours of mild annoyance and a short stint in a girly muumuu.

But ultimately this story isn’t about me. It’s about what you do next and about what happened to a friend of mine who waited too long.

My buddy procrastinated on his colonoscopy until he was 57 and experiencing gut pain. His test discovered advanced cancer requiring extensive surgery.

They operated, and my friend staged a remarkable recovery for three years. But now it seems the cancer is back, with more pain, suffering and surgeries ahead.

Had he done the colonoscopy years earlier, he may well have avoided the cancer.

My primary doctor has pestered me nearly once a month for years to get this done. But my buddy’s cancer was the visceral motivation that moved me past my silly anxieties and fear.

The bottom line? A colonoscopy is no big deal in the end. But waiting too long can be a big deal. The only thing we have to fear is just fear itself — and those silly muumuu hospital gowns. The procedure was easy and the results reassuring.

So what’s next for you? Feeling lucky, or would you rather know for sure? A 50-percent payback on life is a great return for investing just one day of your life.

Gary Horton is a Santa Clarita resident. His column reflects his own views and not necessarily those of The Signal. “Full Speed to Port!” appears Wednesday in The Signal.