Royal Wedding Nerves: Will Kate Middleton Get Cold Feet?

April 26, 2011— -- On Friday, April 29, Lisa Libertini and her fiance, Bill Morse, will exchange their wedding vows in Havre de Grace, Md., just hours after Prince William and Kate Middleton have sealed theirs with a kiss.

"I'm not 100 percent ready to get married," said Libertini, a 30-year-old cash officer. "I have asked my fiance every day for weeks if he wants to back out. I think the only thing keeping me in this is his mom and alcohol."

She said for the past two weeks the couple has been fighting and the pressure of planning their riverboat ceremony, which is only days away, is getting to her.

All couples have pre-wedding jitters, even the royals.

Watch a special "20/20" Thursday at 8 p.m. ET for a behind-the-scenes look at the life that awaits Kate Middleton, and join us again at 4 a.m. Friday for ABC News' live coverage of the Royal Wedding with Diane Sawyer and Barbara Walters.

When a British television show interviewed Lady Diana just days before her marriage to Prince Charles in 1981, the bride-to-be said she wasn't nervous about the walk down the aisle at St. Paul's Cathedral. "No," she said. "I get to go along with everybody else."

But by the end of the 15-minute interview going over the guest list and wedding details, Diana was "almost in fetal position, hunched in her chair, her arms wrapped around her middle, pulling distractedly at the fabric of her sleeves," according to the Telegraph newspaper.

Princess Diana and Prince Charles divorced in 1996, just a year before she was killed in a Paris car crash. Today half of all American marriages end in divorce.

Chances are Kate, who like Diana is marrying into the world of royalty and high expectation, is having pre-wedding nerves, say experts.

"In this situation with huge crowds and people all over the world watching her, I assume she has pretty severe jitters," said Jessica Barry, a wedding planner with Encore Creative in Tempe, Ariz.

"And there is the Princess Diana story, how she was so loved, and quiet and elegant and how she died tragically," she said. "Something in her mind must be feeling the pressure."

The jitters are common. "Sometimes the girls get extremely stressed out and go into Bride-zilla mode and the guys get all laid back and say they don't care, but they they want to know every detail about the wedding," said Barry. "They feel like they are in a completely foreign land."

Barry has shepherded more than 2,000 couples through the planning process and at least 60 have had feet cold enough to walk out -- some within 30 days of the wedding.

Since the economy turned sour, Barry said four to five couples a month change their mind. "I don't know if it's the finances or the pressure," she said.

Barry was working with one bride two weeks before the wedding when the groom-to-be bolted.

"I called the bride for final head count," she said. "She he was handling all the RSVPs. I called the groom to see how it was going. He said, 'I don't know how to tell you this, but I am no longer in Arizona. I just left. I walked out.' "

"We were all dying," said Barry, who had to break the news to the bride. "The poor girl. I told her I would take responsibility for calling the guests and venues and vendors, and I recommended she take the honeymoon. Better it was now than later."