When you gotta go, you better go!

Just ask “Survivor” host Jeff Probst — he found out the hard way that putting off trips to the bathroom can lead to agonizing health problems.

Although in six seasons with the CBS reality series Jeff has been zapped in the genitals by a jellyfish, stung by a scorpion, had a run-in with a king cobra snake and nearly fried himself by urinating on an electric fence, his latest and worst ordeal was surviving a badly enlarged bladder that doctors initially misdiagnosed as prostate problems.

The slender, dark-haired host underwent numerous — and painful — catheterizations, took prostate drugs and lost a shocking amount of weight before the real cause of his problems was discovered.

“He went through absolute hell,” said a source close to Jeff, 40.

It was only after he returned from filming “Survivor: The Amazon” and — at the urging of his artist-girlfriend, Kami Lerner — went to the Mayo Clinic in Scottsdale, Ariz., that he found that his bladder had become enlarged from holding his pee during location shoots of the show!

“I kept telling these doctors I used to hold my pee when I was on shoots,” Jeff told radio shock jock Howard Stern. “I didn’t want to hold up production, so I never went.”

The correct diagnosis rescued Jeff from a health nightmare, his friend said.

“He couldn’t urinate and was in pain,” said the source. “Doctors were convinced that he had an enlarged prostate and that he most likely had prostate cancer.

“They had him on a drug called Flomax and one of the side effects of the drug is that you have a decreased sex drive.

“It was definitely putting a crimp in his love life . . . and he was worried sick that he might have to have his prostate removed. He probably lost 15 to 17 pounds because of the ordeal.”

Once doctors realized what his problem was, they urged Jeff to “retrain” his stretched bladder by going to the bathroom every two hours until the organ returned to normal.