now to the cruise nightmare, all of it caught on infrared videos, those very rare cases of passengers who go overboard. Tonight here, one woman who went over the edge seven stories down in the... See More
now to the cruise nightmare, all of it caught on infrared videos, those very rare cases of passengers who go overboard. Tonight here, one woman who went over the edge seven stories down in the darkness of night, bobbing in the water, she lived to tell. Here's abc's reena ninan. Reporter: Nearly 18 million people took cruises last year. And if you were one of them, you probably stood at the ship's railing, enjoying the view and wondered even for a moment what would happen if I went overboard? What you've probably never seen is a vacation video like this. I remember looking over the water, looking at the ship, and the next thing I knew I was falling. Reporter: Sarah kirby is the woman in freefall on the video. It happened just over a year ago. She was on a 30th birthday cruise, miami to jamaica. Sarah, along with her fiance and best girlfriend, are spending the first night of the trip bar hopping. Ending up getting their drink on at the point after night club. Everybody was drinking to excess and I was enjoying it with everybody else on the cruise. Reporter: And honestly, you got pretty drunk that night. Yes ma'am. We decided to leave the bar, go back to our room. The next thing I remember is going out onto the balcony. Reporter: It's 12 minutes past midnight. One second she's holding the rail of deck seven. The next, she's plunging straight down to the unforgiving sea. A shipboard camera recorded it all. She plummets about two stories, slamming into a lifeboat, then dropping another five stories into the water. It's pitch black outside. You're in the middle of the ocean, all alone. I was so scared. I was going to do everything in my power to survive. Reporter: But she's badly hurt. Broken bones in her face, fractured ribs and a torn artery. I remember being in a lot of pain. So I would swim for a little bit, and then I would be out of breath, and I would float in the water with my face up. But then the water would crash into my mouth and I would choke. Reporter: Ten minutes past. They feel like hours. And all sarah sees is the ship sailing away towards the horizon. As you watched the ship fade away in the distance, what's going though your mind? Words can't even describe the feeling I felt at that moment. I just prayed to go over and over again. It's actually one of the rarest events that happens on cruise ships. A rate of one overboard for every 1 in 1.6 million passengers. Reporter: Cruise industry lawyer larry kaye is correct. Few people go overboard. And yet, in the past three weeks, it's happened on no less than five different ships. You don't get blown or swept off a cruise ship. It does not happen. All of these incidents, unfortunately, are accompanied by some reckless or deliberate act. Reporter: Sarah can't say exactly why she fell. But alone in the water, it didn't really matter. Were you panicking? I was most definitely panicking. Reporter: Did you have a sense that someone knows you're overboard? Her best friend as well as another passenger alert the crew right away. And of course, the ship's camera had recorded the whole thing. Why wouldn't the captain just turn around right away? I think that's the million-dollar question. Reporter: Kirby's lawyer michael winkleman claims carnival cruise line personnel searched the ship for nearly 20 minutes before informing the captain. The vessel should have been stopped. They should have been throwing life wings over so that she could have grabbed onto one, and they should have immediately gone and looked at the video. Reporter: According to carnival cruise lines' own records, it's 12:36 before anyone sees the video. Sarah's been in the water for 24 minutes, petrified of sharks and trying to stay afloat. Things would sweep across my foot in the water and I would just try to continue swimming and not focus on that. When you fall overboard, god forbid, and you disappear into the dark, in the deep waters, no one's going to see you. Reporter: Maritime lawyer james walker has seen this sort of thing before. He makes a living suing cruise lines. They may have a closed circuit camera on the deck, but it's not monitored and it's not connected to an alarm. Reporter: Walker is representing the family of jason rappe, a man who didn't survive after going overboard off of another ship. The ships will continue to sail for two, three hours. Reporter: By the time the coast guard searched for jason, they couldn't find a body. But in sarah kirby's case. Ladies and gentlemen, good news. We have found the passenger who went overboard. Reporter: The video gave them a specific time and place. It's 1:43 a.M. When sarah is spotted, an hour and 31 minutes after she fell. The relief of seeing something in the ocean other than me was unbelievable, that something was out there that could help me. And we are now bringing back onboard the vessel. Sfwlr 1:53 a.M., She's back board. What would it take to make rescues at sea happen faster? Dave leone says his company, radio zeeland, has got a ship shape system already. What we have is a camera, a laser sensor and software that is attached to a screen behind us. Reporter: So I guess you need someone to jump off the boat to demonstrate? If you're up for it. Reporter: To see how it works. I would take the plunge. Here we go! Okay. Lets do it. Reporter: Okay, three, two, one. Here I go. By the time I hit the water, an alarm is sounding. And the system indicates exactly where I went overboard. From this demonstration, it seems like it works. So, why don't cruise ships use it? That's the question we've been asking. The vendors of these systems are very anxious to bring them to market. You can have birds set it off. You can have debris of any kind floating in the air set it off. These detection systems are not perfected. Reporter: Obviously, this demonstration was on a boat, not a giant cruise ship, and on calm water. Carnival cruise lines, the industry's largest, tells "20/20" extensive testing at sea has yet to reveal any system that meets its standds. In fact, few ships have one. Our parent company, disney, tells "20/20" it does have the technology on its ships. As for sarah, she is recovering. But even though the ship saved her life, she hired a lawyer and is suing. You are suing the cruise line that did ultimately rescue you within a short period of time. And she was, by her own admission, intoxicated. Is this suit really fair? Absolutely. 100% fair. What carnival did was wrong. They overserved her alcohol, and when she went overboard, they had awful policies and procedures in place. What's the point of having a camera if there's no one there watching it? Reporter: In a statement to "20/20," carnival cruise lines says that the claims in this suit "are completely unsupported and contradicted by the evidence in the case." I call it sail and sue. We deal with it all the time. I think cruise ships are probably the safest vacation option available to most people. For me, the only safer vacation option would be in my backyard. Reporter: No word if sarah's next vacation will be in her backyard, but it's a sure bet she won't be cruising again anytime soon.
This transcript has been automatically generated and may not be 100% accurate.