Awake at 3am: why it happens and what to do.

You're asleep by half ten, no trouble. Then your eyes open and the clock says 3:12. Within a minute you're in tomorrow's meeting, the unpaid invoice, the unanswered email.

You check the time and count the hours left. I hear this a lot from the business owners and managers I work with, and most blame their mind. The mind comes second. First there's a body that takes very little to wake at that hour.

How to spot it

• Always the same time. Between three and four, like clockwork.
• Wide awake at once. Alert, sometimes with your heart racing a little.
• Your mind goes to work. Problems you handle by day look enormous in the dark.
• You drop off again late. Around half five, just before the alarm.

Why three o'clock

The night runs in cycles of about ninety minutes, four to six a night. At the end of each your sleep turns light, and waking for a moment is normal. You won't remember it. At three, though, three things line up.

Your deep sleep is done. Nearly all of it sits in the first half of the night. The second half is lighter, full of dreams, and easily broken.

Your body is gearing up for morning. Cortisol, the hormone that gets you going, climbs to its peak between four and six. If it was still high at bedtime because you never switched off, it gets a head start. An engine left ticking over needs only a touch.

Your thoughts finish the job. Your body reacts to an imagined problem as it does to a real one. You think of the client, your heart speeds up, and now you're properly awake.

What to do, in the evening and at 3am

A glass with dinner, then stop. Alcohol knocks you out sooner, then breaks up the second half of the night, the dreaming half. One glass, not three, and no nightcap.

Bedroom between 18 and 20 degrees. In the second half of the night your body regulates its temperature less well, so a warm room wakes you more easily. Turn the heating down and use a lighter duvet.

Carbs at dinner too. Keep it light and finish at least three hours before bed. If you're under pressure, a protein-only dinner can leave you wired. Add some rice, potatoes or pulses, which help some people wind down, and see how you sleep. Last coffee straight after lunch.

Empty your head onto paper. Before bed, write down whatever's on your mind and leave the notebook within reach. If a thought turns up at three, two words and let it go. On paper, it no longer needs remembering.

Awake? Leave the clock alone. Breathe slowly: two breaths in through your nose, the second short, then a long one out through your mouth. One to three times. Still awake after twenty minutes? Get up. Another room, low light, a few pages. Go back when you're sleepy. Lie there forcing it and your brain learns that bed is where you worry.

Pick the one that costs you least and stick with it for two weeks. Tomorrow's decisions go better with a full night behind you.