In certain cases - SCUBA diving, for example, it can even put the individual in real danger. Throwing up into an air-providing mouthpiece, for example, can not only be scary, it can be life-threatening.

But what do we really know about seasickness - and is there a real cure for seasickness?

Well, we know that it is most often caused by the confusion of visual cues coming from the eye that tell the brain things are stable, and internal cues - particularly those coming from the centre of balance, in the inner ear - that tell the brain that things are in fact moving.

When we are at sea and look at the cabin or hold, for example, it seems to be unmoving and fixed. But our inner centre of balance informs us otherwise -- and the effect is that confusion and nausea are produced.

Also, the rising and falling of the ship or boat, the roll, pitch and heave, can produce uncomfortable feelings in the bowels as they press against the diaphragm, and this can further aggravate the situation.

As a consequence, stress hormones are produced which, combined with the natural defensive contraction and tightening of the stomach muscles causes the symptoms that those suffering from seasickness know only too well: shivering and shaking, cold sweats and dizziness, the feeling of blood being drained from the face and head and the intense nausea that so often leads to vomiting.

In a nutshell, we feel seasick.

A useful technique when feelings of seasickness appear is to focus on the horizon, if it is visible. Failing this, it can be helpful to simply lie down on your back, near the centre of the boat or ship, with eyes closed and breathing deeply. Instead of staying below deck, it's better to be out in the open, with the wind blowing in your face.

There are, of course, a number of commercial anti-seasickness preparations available, such as Dramamine or Scopolamine, and many find that ginger capsules, ginger tea, or sucking on a piece of crystallized ginger is of help.

Yet these remedies are far from successful for everyone.

It is here that advanced hypnotherapy can be so effective; helping the brain to process, re-interpret and harmonize input in a balanced manner.

When Kevin Costner was filming his movie 'Waterworld' in Hawaii, for example, he found that no matter what he swallowed or did seasickness took over, causing major problems. His seasickness was causing highly expensive delays in filming. He had already been working with a competent hypnotherapist and so flew him to Hawaii in order to work with him in overcoming his difficulty.

Soon Costner was able to find his sea legs and get on with filming -- without being blocked by seasickness.

Not all hypnotherapists are adequately trained and know how to treat seasickness, however. If you should decide to use hypnotherapy in order to conquer seasickness, it is vital that you select a practitioner who has the necessary advanced training in this area.

Enquire about the therapist's qualifications and training and ask about his or her actual experience in handling this issue.

When the correct kind of hypnotherapy is employed, seasickness really can be brought under control, freeing the individual to enjoy being on or in the water.