JESSICA SIMPSON’s fun-filled Hawaiian vacation turned into a nightmare for the mom-to-be when she suffered a terrifying miscarriage scare.

The “Fashion Star” judge – who just cleared her first trimester with her second child – was on doctor’s orders to take it easy during the holidays. But she overexerted herself during the getaway and collapsed with excruciating abdominal pain.

According to a source, Jessica, 32, and her fiance, Eric Johnson, 33, had just returned to their beachside retreat after a long, exhausting walk along the beach when she was suddenly stricken.

“Jessica let out a bloodcurdling scream, doubled over in pain and collapsed on a nearby bed,” the source continued. “She was crying uncontrollably and really feared she was losing the baby.”

Also on the trip with Jessica, Eric and their 8-month-old daughter Maxwell were Jess’ mom, Tina, sister, Ashlee, and Ashlee’s son, Bronx, 4. With their help, Jessica worked through the pain and eventually felt well enough to continue with the vacation.

Jess – who announced her new pregnancy on Twitter on Christmas Day – had gone to Hawaii with her family to escape the pressure she’s been dealing with at home, including her father Joe’s recent confession that he is gay and her parents’ divorce proceedings.

“She has been so stressed out lately over the scandal that her doctor strongly advised her to get some rest for the baby’s sake,” divulged the source. “Jessica’s been pretty good about follow­ing doctors’ orders, but she overdid it this time.”

Back in Los Angeles, Jessica’s doctor explained that her pain had been caused by a severe bout of morning sickness coupled with normal pregnancy cramping.

Now, Jessica and Eric are trying to put the frightening episode behind them.

“They’re happily planning for their expanding family,” the source added. “But they both expect the next six months to be rough.”