You know the feeling. It rises from the bottom of your stomach and swells to a hideous mixture of drowsiness, nausea, the sweats, a loss of colour, headaches, retching and vomiting. Travel sickness affects us all and can ruin any trip, whether at home or abroad. It surfaces on boats, cars, planes and trains - but don't let it put you off your summer holiday. There are a few things you can do to help.