Like eating, drinking and breathing, we need sleep to survive. So how can something that should be so natural, instinctual and automatic be so hard?

As a psychologist who studies sleep for a living, I've worked with hundreds of patients to improve their sleep through cognitive behavioral therapy.

Through my research, I've found that the No. 1 sleep killer isn't social media or an uncomfortable mattress — it's rumination.

Rumination leads to poor sleep

Rumination is a sleep-blocker because it keeps your mind aroused, especially in bed, when it's dark and quiet.

Your attention is drawn back, again and again, to this thing that didn't go well or to a regret. I've laid in bed and replayed a dumb comment I made at a party, even though the person I said it to probably forgot it moments later.

Negative thoughts and emotions like these are what neuroscientists call "salient" because they are so noticeable and loud.

How to stop ruminating and start sleeping better

There's no magic switch to completely turn off rumination. Your brain's job is to consolidate information and build new synapses by dredging up moments and memories from your day — even the things that upset you.

The best time to get ahead of worrying is during the day, when you have important things to do and don't have time to get caught up in mental loops for hours and hours.

Here are two ways to stop ruminating at night — and they only take 15 minutes to do:

1. Worry early.

Set aside aside 15 minutes during the mid- to late-afternoon just for yourself. I call it my "emotional worry" time.

Make sure you don't get distracted by anything or anyone else. Some of my patients have locked themselves in the bathroom to avoid being disturbed. Some take a walk outside.

Once the timer starts, give yourself the freedom to worry about one topic at a time. Think of it as a to-do list that you go through one by one, except what you're checking off are topics you feel the most anxiety about.

If you find yourself worrying during the day, tell yourself: "Look, I just need to postpone this to the next emotional worry time." Use this same technique if your worries pop up again at bedtime: "I have this scheduled for tomorrow."

Do this two to three times a week until your rumination at night slowly starts to fade.

2. Practice "constructive worrying."

On a piece of paper, create two columns labeled as "Problem" and "Solution." Come up with a short list of current issues you're dealing with. Focus in particular on what you're likely to ruminate about tonight.

Under "Solutions," come up with the next one or two steps you could take to tackle each issue. Remember, the goal is to chart out a plan for how to get started with actionable steps for tomorrow, or within the next few days. You are not solving it completely.

Then fold the paper up and put it next to your bed. Say to yourself: "I have a plan." Some people I've worked with will even reach out and touch the paper.

It may sound silly, but bearing witness to the fact that you've already spent focused energy on these problems can release your mind from puzzling over them at night.

Aric A. Prather, PhD, is a professor of psychiatry and behavioral sciences at the University of California, San Francisco and author of "The Sleep Prescription: Seven Days to Unlocking Your Best Rest." A licensed clinical psychologist, he has helped hundreds of patients improve their sleep using cognitive behavioral therapy for insomnia. Follow Aric on Twitter @AricPrather.

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