Stuck with a big medical bill? Here's what to know about paying it off.

When a surprise medical emergency, such as a heart attack or incident that requires an airlift leads to a bill you can't afford to pay, do not fret. 

There are tried and true tactics to negotiate down the bill's amount, as well as other ways to get assistance paying what you owe.

Here are rules of thumbs to follow when a medical bill gives you sticker shock, according to experts.

File an appeal 

If your insurer doesn't want to pay for treatment you received and has denied coverage of a procedure, find out why.

"It's important to understand the reason for denial," Braden Pan, founder and CEO of Resolve, a company that helps patients save money on medical bills, told CBS MoneyWatch. "We see claims denied all the time for stupid things, like a patient's middle initial was wrong, or their birth date was wrong so the insurance company denied coverage," he said. In cases like that, Resolve can always successfully clear up the claim, he added. 

Other times, an insurance company won't cover the cost of a service that they don't deem medically necessary. All insurers have appeals processes in place. Find out what their process is and file an appeal arguing your case. 

"Very often you can appeal and get things covered, but the success rate is slightly lower," Pan said. It helps to have a doctor or medical provider bolster your case by documenting why what you're being billed for was medically necessary. 

"You want your doctor to weigh in on your side," he said. 

Don't pay sticker price

Consider the total amount of the bill a starting point for negotiations. 

"A lot of times, medical providers' prices are wacky," Howard Dvorkin, a certified public accountant and chairman of Debt.com, told CBS MoneyWatch. 

Dvorkin recalls receiving a bill for a medical incident that required his daughter to be airlifted for treatment. The initial total? $18,000. 

He asked the treatment provider what rate they would have billed his insurance company and said: "That's the rate I'll pay." 

He ended up paying about $5,000, he recalled. "Every provider has the flexibility to reduce rates," he said. 

Ask for an itemized bill to see exactly what you are being charged for. Go through it line by line to identify any errors, such as charges for services you never received.

"Make sure there's not a mistake there. Mistakes are made, people bill for the wrong thing and send bills to the wrong patients sometimes. Don't assume the bill is accurate," Patricia Kelmar,  senior director of Health Care Campaigns for U.S. PIRG EducationFund told CBS MoneyWatch. 

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You could also inadvertently be billed for a medical test that was ordered but that you never received, for example. "Those are the kinds of things you might be able to flag and have removed," Kelmar added. 

It's also worth asking the hospital if paying a lump sum, as opposed to paying a bill off in small chunks over time, will earn you a discount. 

"Talk to the hospital and ask if they'll accept a lower amount in exchange for a lump sum settlement," Pan of Resolve said. "If you owe $5,000, say, 'I'll give you $2,500 right now if we can consider this settled and paid in full.'"

Make consistent payments, avoid credit cards

Large medical providers like hospitals, in particular, will often take what you give them, according to Dvorkin. Pay what you can afford on a monthly basis, and it will be applied to your balance.

"As long as you continually pay something, they usually wont turn it back," he said. "If you owe $1,000 and you can only afford $25 a month, guess what, they're going to take it."

Do not use a credit card to pay off medical debt unless you plan on paying the bill in full at the end of the month, because carrying a credit card balance is costly, while unpaid medical bills don't charge interest. 

"Most medical bills, even if they're delinquent, will not charge an interest rate. So putting medical bills on credit cards is not a great idea," Dvorkin said. 

Hardship programs

All nonprofit hospitals in the U.S. are supposed to offer financial assistance programs to help patients who cannot afford to pay for their care, according to Kelmar.

Ask your provider if you are eligible for a discounted care program, Dvorkin advised.

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Eligibility criteria vary, and they can be difficult to identify, so it pays to do your research on your provider's program.

They can be cumbersome to navigate and require lots of paperwork, but can save patients thousands of dollars.