Whenever you sign up for a dive course, you must fill out a medical questionnaire. It will usually include a list of medical conditions that might require a doctor’s clearance before you can commence your in-water training. It’s important to not only fill out the questionnaire honestly, but also to check in with your medical professional if your health status changes to ensure your safety while diving.

Serious dive accidents like collapsed lungs and decompression sickness require medical clearance before returning to the water. But there are other, less well-known conditions that could also require medical clearance before you get in — or back in — the water. Although you may not think they’re serious at the time, honesty is still the best policy. Here are a few medical conditions, some relatively minor, that could affect your safety underwater.

Patent foramen ovale (PFO)

A patent foramen ovale (PFO) is a small opening between the right and left upper chambers of the heart (atria). Everyone is born with this and it closes after birth in about 80 percent of the population. The 20 percent of people with PFO usually have no symptoms and don’t even know they have the condition, but it could put them at a higher risk for DCI. According to the Mayo Clinic, “in decompression illness, which can occur in scuba diving, an air blood clot can travel through a patent foramen ovale.”

Gastroenteritis with vomiting and diarrhea

Also known as stomach flu or traveler’s diarrhea, gastroenteritis is quite common. If you suffer from a bout while on a dive trip, do not brush it off. Gastroenteritis can cause severe dehydration and the symptoms (vomiting and diarrhea) are not conducive to diving. Furthermore, the medications you may take to deal with nausea, vomiting and diarrhea can have undesirable side effects like sedation. If you’re sick, stay out of the water.

Chronic reflux

Chronic reflux, also known as Gastroesophageal Reflux Disease (GERD), causes chronic heartburn and indigestion when acid or food from the stomach flows backward into the esophagus. Although most of us occasionally experience mild heartburn, if it happens while diving it could be detrimental to you. According to Divers Alert Network, “if reflux of gastric contents occurs while one is diving, a diver could be at significant risk. Aspirating food or acid into the lungs or into the regulator could be fatal.” They recommend that individuals with significant reflux should not dive. Speak to your medical practitioner if you experience significant reflux.

Liver cirrhosis

Liver cirrhosis is a degenerative disease wherein healthy liver cells suffer damage and scar tissue replaces them. This is usually caused by toxic substances (like alcohol) or viral infections (like hepatitis). Your medical professional can advise you whether it is prudent to dive with cirrhosis based on your symptoms.

Anemia

Any blood disorder that can affect transportation of oxygen in your body, as well as the degassing process, places you at a higher risk of getting DCI. Anemia could also lead to hypoxia. If you suffer from anemia, consult your medical professional before diving.

Honesty is the best — and safest — policy

It can be tempting to answer “no” for a question that doesn’t seem like a big deal, especially when you’ve traveled so far to dive. However, you must be completely honest when you answer these questionnaires. Refresh your memory when it comes to some of the lesser-known conditions listed on these forms and answer truthfully.

If you are unsure of whether you are fit to dive, skip the dive. It’s far better to cancel a dive than put yourself and other divers in danger. The best policy is to speak to your medical professional before you leave for your trip if you have any questions or concerns. That way you can both be honest on your questionnaire and safely enjoy your dives.