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1. Deep Vein Thrombosis
Deep vein thrombosis (DVT) can develop after long periods of sitting or lying still, causing blood to pool in the legs instead of flowing upward to the heart. Flying or driving long distances has been linked to the development of these blood clots. This can be symptomless or lead to swelling and aching, and in a worst-case scenario, the clots can break off and travel into the pulmonary circulation system.

Fortunately, there are several ways to lower the risks of developing these clots. No matter what your age or level of fitness, it's always a good idea to get up and walk around every couple of hours, even if that just means going up and down an airplane aisle. In between, try some simple exercises to keep your legs mobile and flexible while sitting. That includes raising and lowering your heels while keeping your toes on the floor, and then reversing to raising and lowering your toes while keeping your heels on the floor. Another trick is to tighten and release your leg muscles to stimulate blood flow. Compression socks are also helpful because they're tightest around your ankle and gradually loosen toward your calves and thighs, to help push the blood upward.

2. Norovirus
Although it sounds exotic, Norovirus is nothing more than a simple gastrointestinal illness that is often mistakenly referred to as the stomach flu (a misnomer because it is not caused by the influenza virus). Symptoms can include diarrhea, vomiting, low-grade fever and chills. The biggest concern with contracting Norovirus is that it can lead to severe dehydration and have a stronger effect on the elderly or those with compromised immune systems.

The bad news is that it's highly contagious, and certain travel scenarios are conducive to spreading this condition rapidly. According to the CDC, about 20 percent of outbreaks take place on cruise ships, due to the fact that they involve up to several thousand passengers in closed quarters with many high-traffic, public surfaces.

The good news is that both travel providers and travelers themselves have become more vigilant about communicable diseases (thanks to some highly publicized outbreaks of Norovirus and even the H1N1 scare a few years ago). In this case, a little common sense goes a long way: Wash your hands frequently, including before and after using the bathroom or using self-serve buffets; cough or sneeze into your arm, not your hand; travel with antibacterial gel to use on your hands and wipes to clean off surfaces like doorknobs and remote controls; and, believe it or not, many cruise lines are encouraging passengers to avoid shaking hands, even suggesting a more casual "elbow bump" to avoid contamination.

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