Yes definitely be careful of dehydration. You can buy travel sickness tablets that are made from ginger that are also good for morning sickness, you can buy them in the chemist. Have you tried drinking ginger beer (try it flat) or I think you can get a ginger cordial too. Ginger is a very good natural way to ease m/s and nausea. Try nibbling on some ginger biscuits too. But if it does persist do talk to your GP or midwife about it.