'Mal de mer' as the French would say, is basically motion sickness. The disconnect between what your eyes are seeing and what your balance receptors are telling your brain. It causes the body to react and it makes you feel nauseous and sometimes vomit.
In itself this is nothing but unpleasant, although in severe and prolonged cases it can cause dehydration and therefore result in further complications. It is therefore imperative that you keep an eye on a sufferer and encourage them (without nagging) to keep sipping water even if they are feeling very ill. Remember too, if you are taking medication, including the contraceptive pill, that you are in danger of losing its beneficial effects after a bout of vomiting.
This goes for seasickness pills too of course, so the trick is to take pills the night before you are setting sail to allow time for them to start to work. Patches worn behind the ear can work well, but as with all drugs they have some side effects in certain cases. The benefit to patches is that you won’t throw them up - unless you misread the instructions and swallowed them in the first place!
If you suffer in cars or on flights, it is more likely that you will need to medicate when at sea in rough weather. Common sense would suggest that if you already know that you suffer, be prepared. Most people are not sea sick, although some worry themselves unnecessarily about it.
The best and guaranteed preventative method is to sit under an oak tree, but given that oak trees are few and far between in the Straits of Gibraltar, that could be a problem. Whether you suffer or not, rest assured that they say there are only two types of people in this world; those that suffer from seasickness and those that have yet to suffer.
The bad news
Lord Nelson was sick every time he went to sea and he was quite a decent sailor by all accounts. The bad news is that there is no absolutely guaranteed preventative measure available in capsule form, but there are plenty of effective medications on the market. Only a small percentage of people suffer in normal sailing conditions and they recover quickly once ashore. If you do suffer, don’t worry, we’ll monitor you and make sure you’re OK.
The good news
Most people rarely suffer - and even when they do, fatalities are few and far between (joke!).
Most are only ill when it's pretty rough and even then, only for the first 24 - 36 hours of a trip. Our RYA Competent Crew and Day Skipper Courses mostly consist of day and evening Sailing between ports and perhaps some short passages. Therefore, if you find you suffer from seasickness, your suffering is likely to be short lived. Either way, don't worry - trust me - it will stop, eventually!
In any event, like so many things at sea, look after yourself and look after your crew mates and be considerate of those suffering - you might be next!