The first time Gregg Casarona ever had sex, the walls didn’t just shake — they shattered.

The 440-pound project manager was 21 at the time and had been dating his girlfriend Jen Gerakaris for about a month when they decided to take things to the next level.

Welcome to the new TLC series “Sex Sent Me to the ER,” premiering Dec. 28.

Gerakaris was 22 and living in her parents’ Long Island basement at the time. She made her move by stripping down to her bra and panties and waiting on her bed until Gregg got the hint.

“I knew he was a virgin and I honestly didn’t care,” Gerakaris says. “We were dating for a little while and he hadn’t put any moves on me yet so I made a move.”

When things began to heat up, Casarona thrust the 110-pound Gerakaris backwards with all 440 pounds of his girth. And Gerakaris’s head went right through the basement’s sheet-rock wall.

“My initial reaction was, ‘I killed her,’ ” Casarona tells The Post. “‘This is my first time. And Jen is dead.’”

After a couple of terrifying seconds, Gerakaris slowly pulled her head out of the wall and looked at Casarona incredulously.

“Why’d you stop?” she asked.

“He looked like he was about to have a heart attack,” she says. “So I just wanted to lighten the mood.”

But Gregg was shaken and insisted on taking his lover, who started to become dizzy and nauseous, to the hospital. She was diagnosed with a concussion.

Although Gerakaris and Casarona were shy about telling the doctors and nurses about what caused her injury, the pair will be sharing their tale on national TV next week.

Their story will be featured — with a PG-13-rated reenactment — in the premiere episode of “Sex Sent me to the ER.”

After bringing down the house, the couple says they were a little bit more careful about their positioning during sex.

“In the beginning, there were lots of pillows and we didn’t do it anywhere near a wall,” Gerakaris says.

The couple stayed together for four more years after their ER trip and remain close friends today. Casarona, now 28, has since dropped 220 pounds and Gerakaris, now 29, has a new beau who knows about that wild night.

“I was friends with him before and, of course, our friends know the story,” Gerakaris says. “It’s a story we always tell over drinks.”

“But our families? No, they don’t know,” Gerakaris says with a laugh.

“My parents didn’t even know about the wall. I had Gregg fix it and thank God I still had matching paint.”

The pair is just hoping their parents don’t happen to tune in next week.

They say Love hurts

Gregg and Jen aren’t the only lovebirds who have landed in the hospital. Here are five other cases featured on TLC’s “Sex Sent Me to the ER”:

1. Rock singer and guitarist Cash O’Riley and his girlfriend Anne shared a night of passion. During his orgasm, Cash collapsed onto Anne, losing feeling in his left arm and leg. Turns out, Cash had a stroke mid-shag.

2. Dr. Kevin Klauer once treated a man who broke his penis during a threesome with his wife and mistress. When the two women began brawling at the hospital over who did the damage, Dr. Klauer got a bonus patient to treat.

3. Liz and Eric had a quickie before work one morning. But when Eric got up to leave, Liz was still having an orgasm. Pleasure turned to pain when it continued for two hours.

4. When Tsion and Brashaad snuck away for a jaunt in the janitor’s closet, the tight space resulted in injuries.

5. Dr. Jordan Moskoff treated a man for broken bones after he claimed he fell washing his windows. But the man was naked when he fell. When his wife showed up, she accused him of cheating.