Motion sickness, or travel sickness, occurs when the movement of a car, train, or boat you are traveling in causes a mismatch between the signals from the balance sensors in your ear and the sense of balance you get through your eyesight. Think of being on a boat - it feels like it's rocking (the sensor in your ear tells your brain you're in motion), but when you look at the horizon, it's flat and still (your eyes tell your brain that you're stationary). This mismatch can cause some people to have symptoms of nausea, dizziness, headaches, and feeling genuinely unwell. If you are on a mode of transport for more than a couple of days (such as on a cruise), the majority of people will find their body adapts, and the symptoms improve. It is not known why some people suffer from motion sickness more than others. It is more common in women and people who suffer from migraines. It is also very common in children; however, the majority will grow out of it through their teenage years.

Altitude sickness is also known as acute mountain sickness. Altitude sickness can happen to anyone, no matter your fitness level, age or experience. It affects your breathing and your ability to take in oxygen. This can be life-threatening. It happens when you travel to a higher altitude too quickly, typically greater than 2500 m (about 1.5 miles) above sea level, often when mountain climbing, but also in cities that sit high above sea level.