--Updated by Jeannine Williamson, Cruise Critic contributor

When we plan our next cruise, we have blissful thoughts of diving into calm blue waters and endless plates full of delicious food. Being stuck in our cabins with an upper respiratory infection or the dreaded norovirus, or sent to a hospital with a broken leg or heart attack? Umm, not so much.

Because cruise ships are essentially floating cities, major lines contain infirmaries with staff available 24 hours a day to care for passengers. These facilities are typically equipped to treat only minor nonemergency conditions. If your illness is serious or you find yourself needing emergency treatment, you'll be referred to a facility on land and disembarked to get care.

Here's a look at what to expect regarding cruise ship doctors and medical facilities, procedures and policies if you get sick on a cruise. If you're trying to stay as healthy as possible on your vacation, read our advice on how not to get sick on a cruise.

Cruise Ship Doctors

Ships from the main cruise lines all will have at least one doctor and two nurses onboard. Many larger ships sail with two doctors and three or four nurses. According to American College of Emergency Physician guidelines, ships must have medical staff on call 24 hours. Medical personnel (both physicians and registered nurses) must have at least three years of postgraduate experience in general and emergency medicine or board certification in emergency medicine, family medicine or internal medicine.

To get an idea of the staff's credentials, consider that Carnival Cruise Lines requires that its physicians be registered in the United States, United Kingdom, Canada, Australia, New Zealand, Ireland, South Africa, a European Union country or any other country approved by the fleet medical director. Medical personnel also must have completed the required number of years of training in a recognized school of medicine.

The staff must be able to perform advanced life support practices, emergency cardiovascular care and minor surgical procedures. They are expected to stabilize seriously ill patients, perform reasonable diagnostic and therapeutic interventions, and help evacuate seriously sick or injured patients. Doctors and nurses also are required to be fluent in the predominant language of the ship.

Cruise Ship Medical Facilities

If you're injured or become ill, you might need to visit the cruise ship's medical facilities. The infirmary is usually located on a lower deck. While it generally will have regular hours, shown in the ship's daily program, staff are on call 24 hours for emergencies.

The ship's medical center contains several beds and is set up to treat minor nonemergency conditions or to stabilize passengers facing life-threatening conditions. Ship doctors and nurses are most likely to deal with passengers suffering from respiratory (influenza) or gastrointestinal (norovirus) illnesses, motion sickness or injuries, the World Health Organization says, adding that it is important to view the ship's medical facility as an infirmary and not as a hospital.

Cruise ship medical facilities must adhere to the standards set by the American College of Emergency Physicians. The ACEP guidelines dictate that the infirmary must contain the proper equipment to handle a range of treatments and diagnostics. Among its equipment, the facility should have wheelchairs, a stretcher, back board for spine immobilization, lab capabilities for tests, oxygen, EKG capability, two defibrillators, cardiac monitors and other equipment to gauge vital signs.

The Cruise Line International Association, the world's largest cruise industry trade organization, also sets standards of care for its member cruise lines.

The U.S. Centers for Disease Control and Prevention says ship infirmary capabilities vary depending on size, length of sailing and passenger demographics. The CDC compares shipboard facilities to ambulatory care centers.

Onboard Pharmacies

Pharmacy stocks are available onboard, which means you will be able to get basic medicines. The size of the inventory varies by ship, but staff will be able to provide you with antibiotics, seasickness pills (often complimentary), aspirin and other common medicines. The pharmacy stocks typically will include medications for gastrointestinal and cardiovascular issues; respiratory problems; infectious diseases; eyes; ears, noses and throats; and urinary tract, as well as vaccines.

The cost of these meds will be more than if you shopped at your home pharmacy but about the same as getting off the ship and buying them in port.

Quarantine Procedures

Cruise ship policies dictate that if you feel like you might be getting sick or have signs of a serious ailment, such as vomiting or diarrhea, you must tell the ship's medical staff immediately. Passengers can be restricted to their staterooms if the ship's physician decides their illness poses a risk of outbreak. Cruise lines are especially wary of influenza or the highly contagious norovirus, which can quickly spread.

If norovirus is suspected, crew will enact measures to isolate you from other passengers. You will be told that you must remain in your cabin, and your key card will be deactivated to discourage you from attempting to leave. The quarantine is not just a suggestion; the lines take this seriously. Cruise lines' guest conduct policies outline consequences for not adhering to the conditions -- security staff or law enforcement may intervene, or you could be banned from cruising with the line in the future.

When under quarantine, you typically will be required to remain in your room and take all your meals there until you are symptom free for 72 hours. Crew will bring you meals, drinks and anti-nausea medication, but you are not to leave, even if you're feeling better.

Medical Emergencies

If a life-threatening injury or illness, such as a serious fall or heart attack, occurs, cruise ship doctors are unlikely to fully treat a patient onboard, choosing instead to send the passenger to a land-based medical facility. Make sure you have up-to-date insurance and any contact information for your carrier and primary care physician available, in case you're faced with an emergency.

Cruise line policies outline conditions under which passengers should be medically disembarked. The ship's medical staff has the right to determine whether a passenger is unfit to continue on a sailing. Cruisers will be disembarked if they are in a condition "likely to endanger health or safety," according to MSC Cruises' conditions of travel, for example. Cruise doctors can make arrangements to have passengers transferred to a health facility at any port, at the passengers' expense.

In dire cases, a patient might need urgent care that can't be administered onboard. Sometimes the only option is to evacuate a passenger by helicopter for transportation to a shoreside medical facility. (This is often carried out by the Coast Guard in the U.S. and sometimes a foreign military when you're overseas.) Evacuation by air is typically reserved for only the most critical cases because the procedure can put the patient under added physical and emotional stress. The medevac units are staffed by medics who are expertly trained in emergency treatment.

Some cruise lines also utilize telemedicine to assist patients. The technology allows physicians to connect to shore to access specialists and data that can help treat patients onboard. 

Paying for Medical Care While Cruising

When you get sick or worse and need treatment or emergency services, you will pay for it, typically out of pocket. If you receive treatment or medicine from ship physicians, the cost will be charged to your cabin folio. If you are medically disembarked and sent to a shoreside hospital, you will likely need to pay in cash.

Travel insurance can help mitigate the costs and alleviate any worries you have before starting your cruise. You would start by filing a claim with your personal insurance carrier to recoup what's covered by your health policy. Travel insurance, which usually costs between 5 and 8 percent of the total cost of the trip, would cover the rest. In addition to medical costs, you can buy trip insurance policies that cover a wide range of trip interruption and cancellation situations, as well as evacuation and repatriation of remains should the unthinkable occur.

Robust travel insurance policies can be a financial lifesaver if an expensive emergency procedure, such as evacuation from the ship and a hospital stay in a foreign port, is necessary. Also consider that transportation to a full-service hospital from a remote cruise location like Greenland or Antarctica can be extremely costly.