There you are, snoozing away contently and then suddenly - bam! You wake up with the most horrific pain in your leg, like every muscle is being ripped from the bone. Assuming that you're not sleeping in the jungle and a tiger has just taken a fancy to your lower limbs, it could be that you're experiencing cramp. If so, you'd almost certainly like to know how to stop the pain first and then learn how to reduce the chance of this happening again later.

Stop the Pain!

The first thing you should do is stretch the contracted muscle. Try to stand up and straighten out your leg and massage your leg to get the blood flowing. The muscle may try to contract again almost instantly so keep it straight and continue to massage it for five or ten minutes. If your agonised screams have woken up your partner, you may be able to get help with the massaging bit.

A bout of cramp can be very distressing, so if you're looking after someone who's suffering from cramp, you'll want to be as calming and sensitive as possible. Oh, and forgiving - they might say a few words and phrases that they'll regret later. Just remind yourself it wasn't them speaking, it was the cramp that possessed them.

What Just Happened?

This is the easy bit. One of your leg muscles flexed and remained tight for a while, an involuntary contraction that can be agonising, especially if it wakes you up. The like culprits are the gastrocnemius (your calf muscle, at the back of your lower leg), the hamstrings (back of the thigh) or the quadriceps (round the front of your thigh).

Why this happens is another matter. The main problem with involuntary reactions like this is that they're difficult to replicate so that they can be studied. There are, however, enough theories about why it happens to give us a few pointers.

So, Why Did it Happen?

There are many reasons why you might suffer cramps. It can become much more common during pregnancy due to significant changes in calcium metabolism. It also becomes more common as you get older. One of the most common causes though is being over-weight. All of the advice books will say things like 'You need to do more exercise' or 'You haven't been taking in enough oxygen', but it comes down to the same thing - all those years of dodging salads and avoiding the daily jog are going to take their toll.

Now, of course healthy people get cramp too, but as they're already well aware of the importance of exercise and probably don't need an entry such as this. For the rest of us though, here are a few tips:

• If you do exercise regularly, you might not be doing it properly. Remember to warm up beforehand and cool down afterwards with stretches to loosen the muscles. You should vary your exercise as repetitive movements can also lead to cramp. You also need those off days to avoid over-exerting your muscles; muscle fatigue can sometimes be just as bad for you as no exercise at all. You should also ensure you don't dehydrate.

• You're likely to suffer from cramps if you have low levels of magnesium, potassium, calcium and sodium, or a raised level of lactic acid. You might sweat the nutrients out while exercising, though alcohol, fizzy drinks and fatty foods can also reduce your magnesium levels significantly, make you sweat and lead to those agonising pains in the middle of the night. Eat a banana or two - they're a good source of potassium.

• Shortage of oxygen can also be the cause of cramps, often the result of Adult Sleep Apnoea, though over-exertion, or sitting or lying in an awkward position.

• Another cause could be a medical condition called 'Intermittent Claudication', again a shortage of oxygen, due to cholesterol plaque built up in the arteries of the legs. Patients who have claudication are at extremely high risk for suffering a heart attack or stroke.

So, if you've had a night of drinking, picked up a takeaway on the way home, fallen asleep in an awkward position and slowly started to sweat out the booze, you may find you get woken up by an attack of cramp.

What Can I Do to Stop it Happening?

Drink water. You should be aiming for about eight glasses (or two litres) of water a day. If the cramps recur, it's always best to go to your doctor and get a check-up. Though cutting down on the curries and beer won't hurt either.

Your doctor might prescribe quinine, but some people have found that homeopathic remedies can also help. Substances such as arnica, calcarea, camphora and cuprum are thought to be good. You can also get magnesium supplements.

One other final tip - raise the foot of your bed by about 10cm. This will apparently help your circulation and increase the likelihood that you'll sleep in a healthier position.