As a graduate student pursuing a degree in theology twelve years ago, I took a course called Systematic Theology–by far my toughest class–by a brilliant professor who was dying of bone marrow cancer. No one knew she was dying. She kept her diagnosis to herself and, as best as she could, covering up her chemotherapy and radiation treatments.

One afternoon she gave us this assignment: If you had only one day left of your life, how would you live it? What would you change about your life now?”

“I would drop this course,” I immediately thought to myself.

The responses were fascinating. Some people would totally rearrange their lives. A woman who worked in the admissions department said she would quit her job and start writing. Others wouldn’t adjust a thing. I was somewhere in the middle: I felt like I was generally going in the right direction, but I could certainly do without researching the Holy Trinity, because it was a mystery after all.

I can’t help but think of that assignment as I read about all the cancer stories in the news these days: Elizabeth Edwards’ cancer has returned, and is incurable, and White House press secretary Tony Snow, after beating colon cancer two years ago, is now battling the same cancer that has spread to his liver.

As a depressive, I learn a great deal from persons suffering from terminal illnesses, because, like them, I’m never totally separated from my disease. The persistent sucker stalks me more than the lady who wants my parking space at Whole Foods, waiting for an opportunity to poke out its unsightly head. When I’ve reached a good place with my depression, I consider it merely a remission. And like cancer patients, I believe that my breakdown has changed me forever, that there is no returning to the blithe and idealistic girl I once was.

The tools that those diagnosed with cancer use to live meaningful lives even as cancer cells metastasize and replace normal tissue in their body are the same rules that help depressives forget about what’s going on in their brains and make the best of their days. After lots of conversations with folks battling various cancers at different stages, I’ve identified these six valuable maxims that they abide by. They are good reminders for me too.

1) One day at a time. Or an hour at a time. Those living by an hourglass can’t afford to get tangled up in the “what ifs” of the future and the “if onlys” of the past. The sick person knows better than anyone that all he has is the moment before him. As Babatunde Olatunji once said, “Yesterday is history. Tomorrow is a mystery. And today? Today is a gift. That’s why we call if the present.”

2) Feel the fear and do it anyway, as psychologist Susan Jeffers says. Or, as Dr. Abraham Low, founder of Recovery, Inc. would say, “Be self-led, not symptom-led.” Cancer experts have found that patients who approach their diagnosis like an athlete at a major competition fare better than those who give up and stop playing bridge on Tuesday afternoons because they are dying. For me, this means “faking it til you make it,” and forcing myself to go to the preschool social hour and pretend I am genuinely interested in hearing how Timmy’s mom potty trained the precocious boy with the M&M and sticker method when I desperately want to curl up on the couch and concentrate on how miserable I am feeling.

3) Build a strong network of support. Family, friends, online buddies, books, therapy, support groups, church pals…all of it. Support not only makes a sickness more endurable, it can increase a person’s chances of recovery and survival.

4) Do what you love. An older friend of mine with as many health problems as I have issues told me that the only way he has survived it all is to keep on doing the things that give him pleasure: writing and talking to retreat groups about Jesus. When people have a mission–when they feel a part of some greater purpose–their recovery rates are better. If a guy loves to fish, he ought to keep on throwing the worms out even on his bad days. And he is empowered by serving soup to the homeless on Saturday mornings or putting out a newsletter about social justice, then he shouldn’t back away from those activities even if he limps with exhaustion.

5) Think positive. I’ve explained in several posts the brain’s “neuroplasticity,” or our ability to change the brain’s structure and neuronal connections with our thoughts. So it doesn’t surprise me that several studies have shown that positive thinking can contribute to stronger immunity, less stress and fewer toxic side effects from treatment. Kevin Stein at the American Cancer Society teaches cancer patients a three-step method to positive thinking: Stop, Think, Focus. When a patient begins to panic with thoughts like “I can’t do this,” he needs to make a conscious effort to say to himself, “Stop!” (At one point I would wear a rubber band around my wrist and snap it every time I panicked.) In the next step, he must pull out any positive aspect about his illness, such as “I’m going to be okay,” or “I have wonderful support,” or “I am a strong person,” and, finally, he must focus on those thoughts.

6) Appreciation. You never fully appreciate what you have until it’s gone. But cancer (and depression) gives you as good of an opportunity as any to try.