First, however, a quick word of warning. We all have sleep-light nights from time to time - but if the problem persists, do seek medical help. 'If you have trouble sleeping for weeks on end and you're dropping off during the day, see your GP,' says Dr Guy Leschziner, consultant neurologist at London Bridge Hospital. 'People with "normal" insomnia typically feel very tired, but not sleepy. So if you're dozing off at your desk or on the train, there may be an underlying cause that requires treatment.'
As tempting as it may be, steer clear of coffee to perk you up. 'Caffeine may boost your blood sugar levels shoot up temporarily - but they will then fall just as rapidly, making you feel even more fatigued, lethargic and irritable,' says nutrition consultant Sana Khan from The Food Doctor. The perfect alternative? Try some lemon and rosemary tea. Consultant aromatherapist Joannah Metcalfe explains: 'The lemon will refresh and revive, while the rosemary stimulates brain function.'
A small bottle of pure peppermint essential oil can provide the perfect pick-me-up for those moments throughout the day when you're really flagging. Joannah Metcalfe advises: 'Inhale directly from the bottle - being careful not to let it touch your nose - and you'll wake up instantly. The essential oil molecules stimulate the olfactory epithelium - the tissue involved in smell - in the lining of your nose, sending an instant response to the centre of the brain. The result? It'll wake you up - and lift your spirits into the process.'
You may feel more creaky than a wobbly floorboard - but this simple exercise from Pilates guru Alan Herdman can reinvigorate and revitalise you before you even venture out of the bedroom: 'Stand with your feet hip-width apart and arms relaxed by your side. Gently lift your head upwards and lengthen the spine. Inhale and lift your arms out to the sides then overhead. Reach your fingertips towards the ceiling, stretching upwards, then relax and drop the shoulders away from the ears. Repeat this upward stretch three times. Exhale and lower your arms back down to your sides.'
Now, we're only suggesting you give your hair a gentle pull - don't yank at it! - but there is good reasoning behind this apparent madness. Registered osteopath and naturopath Nadia Alibhai explains: 'Slowly tugging at the roots of your hair will stimulate the nerve endings and help get the blood flowing to your head, which will make you feel more refreshed. Alternatively, you could simply try smiling. This increases blood flow to the skin, making your face appear more radiant and awake.'
One of the best ways to wake yourself up is to get moving straight away - so try to weave some exercise into your morning routine. 'A drive in the car is never going to do the trick - so why not put in a little effort and walk, jog or cycle at least some of the way to work instead?' suggests personal trainer AJ Perera from Fitness First. 'The fresh air and adrenaline rush will ensure you're alert and fully motivated before 9am.' Aim to keep your energy levels up by going for a brisk walk at lunchtime, too.
Having trouble staying awake on a grey winter's day? Dr Leschziner advises: 'Try to expose yourself to a bright light as early as possible in the day. This will make you feel more alert and should reinforce melatonin release so you sleep better the following night.' Applied physiologist Laura Ginesi from Birmingham City University agrees: 'If you can't get outside in the natural sunlight, make sure you have good lighting indoors and sit in a non-squishy, supportive chair so you're not tempted to fall asleep.'
Avoid the temptation to hit the snooze button - and head for the shower instead. 'After you've showered as normal, stay put and alternate between two minutes of hot water and 15 seconds of cool water, repeating twice,' suggests Nadia Alibhai. 'The changes in temperature will create a pumping action on the blood vessels, which boosts the circulation and gives your body a real wake-up call.' Want another tip for the shower? Joannah Metcalfe suggests: 'Make your own revitalising gel by adding two drops lime, two drops rosemary and four drops geranium essential oils to 15ml fragrance-free shower gel.'
Obviously, falling asleep at your desk or in the middle of a meeting is never a good idea. But even if you do suddenly have the opportunity to take a quick nap in the middle of the day, it may not be such a good idea. Dr Leschziner warns: 'If you really can't resist the urge to nap, limit it to no more than 15 minutes. Any more and you'll enter a deeper sleep, which will make you feel very groggy when you wake up. What's more, it can have an impact on the following night's sleep - and so the cycle continues.'
What you consume throughout the day can hold the key to maintaining energy levels, so try to stay topped up by eating every three hours - even if it's just a snack. Nutritionist Patrick Holford offers these three top tips: 'Eat slow-release carbohydrates, such as fruit, whole grains, nuts and seeds, to keep you steadily fuelled; ensure you have optimal intakes of vitamins and minerals; and avoid stimulants, such as sugar and caffeine.' For an extra boost, start the day with Patrick's nutrient-rich breakfast shake Get Up and Go, £28.25, Holland & Barrett.
You know those eight glasses of water you should be drinking every day? Well, it's even more important to get them down you when you're feeling tired and groggy. Henrietta Norton, nutritional therapist and founder of Wild Nutrition, warns: 'Even mild dehydration can reduce cognitive function by as much as 30 per cent, and energy levels can seriously flag.' And don't just drink cold water: splash it on your face, too! Nadia Alibhai explains: 'The cold constricts your blood vessels and closes larger pores, leaving a sharp burst of oxygen on your skin - making you feel more alert in an instant.'