You’re on vacation in a tropical paradise. There’s music in the air and the umbrella drinks are flowing. You’ve got a dive in the morning but, hey, that’s tomorrow. One more round won’t hurt, right? Wrong.

Too much alcohol leads to dehydration — one of the leading preventable causes of decompression sickness. Remember, diving itself is already plenty dehydrating, as you’re breathing dry air and the diuresis (lots of peeing in the wetsuit) that you get from immersion. Adding to it with a hangover is just asking for trouble.

“Dehydration not only makes you fatigue faster, it also decreases the amount of blood available for gas exchange and may slow nitrogen removal from your body, leaving you at increased risk for decompression illness,” says diving enthusiast Mary Ann Everhart-McDonald, M.D.

What's worse, if you’re hung over, you're already feeling crappy and may be less quick to register key symptoms of decompression illness like joint pain, nausea, fatigue, headache and confusion. “The dehydration, fatigue and lack of judgment make being hungover just as dangerous as being drunk when you're underwater,” Dr. Everhart-McDonald says.

Too much booze also leads to electrolyte imbalance, leaving you fuzzy headed, queasy and fatigued the next day. (Not to mention seasickness is already common enough on the rocking waters.) Being queasy from a hangover increases that risk of seasickness and the dreaded (and far more dangerous) vomiting into your regulator.

As if all that weren’t bad enough, booze messes with your anterior cingulate cortex —the error detection center of your brain. That's really bad business before a dive. And when you’ve had enough to be hung over the next day, that generally means that error detection centre is still not up and fully operational, which puts both you and your dive buddy at risk.

And while we know PREVENTION is the best medicine, who doesn't want to welcome a much-needed dive trip with a cool cocktail? Just be sure to limit your alcohol consumption to two or three the night before a dive. If you do give in to temptation, here are some tips to get back on track.

1. EAT The night before, eat plenty of food with your booze to help slow alcohol absorption and prevent low-blood sugar.

2. DRINK “Order a pitcher of water and drink two glasses of water for every alcoholic drink,” advises Lewis Kohl, M.D., chairman of emergency medicine at Long Island College Hospital in Brooklyn, N.Y.

3. BEDTIME REGIMEN “Preventing dehydration can head off a hangover. If you overdid it, drink three glasses of water when you get home and take Motrin [ibuprofen] to reduce headache-causing inflammation,” says Kohl. “When you get up to urinate during the night, drink more water and take more Motrin.”

4. THE NEXT MORNING If you missed the night-before preventative steps, head off a mild hangover in the morning by getting up an hour or two before you have to, drinking a big glass of water or Gatorade (which replaces potassium and magnesium that are depleted by drinking), take ibuprofen, and going back to bed ‘til you need to get up. If you still wake up bleary-eyed and hairy-tongued, however, skip your morning dive. The ocean will always be there and it’s simply not worth the risk.

And don't forget that you’re still in line for the afternoon dive. Just watch the cocktail consumption this time.