Short on sleep but need a clear head? What should I do?

On a day after a short night, what you can do is simple: give the groggy spell after waking time to pass, get bright light, wash your face, drink water and eat regular meals. If you drink coffee, avoid it from the afternoon and stay within the 400 milligrams a day that the US FDA has cited as not generally associated with negative effects for most adults. Take a nap of under 20 minutes in the early afternoon if you can, and move a little. Put off driving when you feel drowsy, and leave big decisions until later in the day if possible. Then go to bed on time tonight and get up at your usual time, so one short night does not turn into several.

Why does my head feel foggy after a short night?

Short sleep affects how quickly you react and think. Training material from NIOSH, the CDC's workplace safety institute, describes a groggy spell after waking with slower reactions, poorer short-term memory and slower thinking. It typically lasts 30 to 60 minutes, can be longer when you are short of sleep, and has been seen to last up to 2 hours.

Slower reactions and decisions

The CDC says drowsy drivers react more slowly to changing road conditions and make poor decisions, and can have very short moments of sleep without realising it. The same slowing shows up at a desk: you read the same email twice or miss a number in a spreadsheet.

For losing focus halfway through a task, see Why do I lose focus halfway through, and what can I do?

The afternoon dip

CDC NIOSH material explains that the body clock gives a second window of sleepiness in the afternoon, around 2 to 4 p.m., on top of the main one in the early hours of the morning. After a short night, that dip is felt more strongly.

How long you have been awake

NIOSH also notes that the longer you have been awake, the more sleep pressure builds up. The CDC says that after 17 hours awake, impairment is like having a blood alcohol content of 0.05, and after 24 hours, like 0.10.

I slept too little but need a clear head today. What should I do?

Plan the day in small steps, starting the moment you wake up.

Light and a splash of water

CDC NIOSH material lists bright light and washing your face among the things that help you become alert more quickly after waking. Open the curtains as soon as you get up, step outside for a few minutes, or sit by a window for breakfast.

Water and regular meals

The NHS lists being mildly dehydrated among the reasons you can feel tired. Drink water through the day; in hot weather or an air-conditioned office you may not feel thirsty, so keep a bottle on your desk. The NHS also suggests eating regular meals and healthy snacks every 3 to 4 hours rather than a large meal less often.

A short walk

The NHS says even a single 15-minute walk can help you feel more energetic. Walk to buy lunch, take the stairs, or step outside between meetings.

Do the hard work when you feel clearer

If you can choose, avoid starting the most demanding tasks in the first hour after waking, when grogginess may not have passed. Leave routine work for the early-afternoon dip.

Caffeine and naps: what should I watch on a short-sleep day?

Both can get in the way of tonight's sleep, so keep these limits in mind.

Caffeine: amount and timing

There is no need to drink more than usual. The US FDA says 400 milligrams of caffeine a day, about two to three 12-fluid-ounce cups of coffee, is the amount it has cited as not generally associated with negative effects for most adults, but sensitivity varies from person to person. Count all sources toward that total: tea, soft drinks, energy drinks and chocolate also contain caffeine, and the FDA notes a 16-fluid-ounce energy drink can contain as much as 328 milligrams. The FDA lists jitters, anxiety, a fast heartbeat, an upset stomach, headache and sleep disruption among signs of too much.

The NHS says the effects of caffeine can last up to 7 hours, so an iced coffee at 3 p.m. can still be working at 10 p.m. If you drink coffee or tea, avoid it from the afternoon.

A nap: how long and when

CDC NIOSH material says that if you work a daytime schedule, a brief nap of under 20 minutes is recommended, and that a short nap of 15 to 30 minutes can increase alertness for a couple of hours with less grogginess. Waking after about an hour, when sleep is at its deepest, can leave you much groggier. Around 2 to 4 p.m. is a natural nap window. Avoid napping around 11 a.m. to noon and 1 to 3 hours before your usual bedtime, which NIOSH says makes it harder to fall and stay asleep. Set an alarm so you do not oversleep.

What should I be careful about on a short-sleep day?

On a short-sleep day your reactions and judgement are slower, so take care with tasks where mistakes matter.

Driving

The CDC lists nodding off, drifting from your lane, tunnel vision and forgetting the last few miles you drove as warning signs of drowsy driving. If you notice them, pull over somewhere safe and take a 15 to 30-minute nap before going on. The CDC says this helps only for a while and that what you really need is sleep. If you can, take public transport or ask someone else to drive.

Big decisions and precise work

Since the CDC says drowsiness leads to poor decisions, put off signing contracts, large money transfers or difficult conversations to another day if you can. Double-check numbers and messages before you send them.

Alcohol

Alcohol after a tiring day may help you fall asleep, but the NHS says you sleep less deeply after drinking, so you can be tired the next day even after a full night.

How do I get back on track from tonight?

One short night is common. The aim is to stop it becoming a pattern.

Go to bed on time and keep your wake time

The NHS suggests going to bed and getting up at the same time every day. Go to bed at your usual time or a little earlier tonight, and get up at your usual time tomorrow rather than sleeping in for hours. The CDC recommends 7 hours or more of sleep for adults aged 18 to 60.

Keep naps short

Long naps late in the day make it harder to fall asleep. Keep any nap under 20 minutes and before mid-afternoon. If you have trouble sleeping at night, the NHS suggests avoiding naps in the day.

Relax before bed

The NHS suggests taking time to relax before going to bed. Put the phone away, dim the lights and do something calm. If short nights have run on for several days, see Why do I get ill easily after several nights of short sleep?

When should I see a doctor?

Feeling foggy after a short night is common. But the NHS says that if you feel an overwhelming tiredness that is not relieved by rest and sleep, you should see a GP. Also see a doctor if:

• you often nod off during the day even after sleeping enough
• you keep feeling sleepy while driving
• tiredness is affecting your work, study or daily life
• you take regular medicines and feel unusually drowsy, as some medicines can affect sleepiness

Do not start any medicine to stay awake or to sleep on your own; ask a doctor or pharmacist first.