The neurological condition that Lucy suffers from, Goldfield Syndrome, is entirely fictional. True anterograde amnesia affects either short-term memory, which can last minutes or seconds, or intermediate-term memory, which can last days or weeks. Falling asleep has nothing to do with the condition, and sleep actually intensifies many chemical effects which help memory.
In an early scene a dentist and a woman in the dentist's chair are seen talking with each other. The woman playing the dentist is Jackie Sandler, Adam Sandler's wife. And the woman in the chair is played by Linda Segal, director Peter Segal's wife, who actually is a dentist in real life.
The clinic that Lucy visits is called the "Callahan Institute" and Dr. Keats (Dan Aykroyd) states that it is "funded out of Sandusky, Ohio by T.B. Callahan, the automotive components tycoon". In Tommy Boy (1995), Aykroyd plays a rival automotive components tycoon that is attempting to purchase Tom (T.B.) Callahan's company.
The diner where Lucy has her breakfast every morning was originally a house that was remodeled for the movie. It is located on a macadamia nut farm on the eastern side of Oahu. The same house was used in Tears of the Sun (2003) and scenes from Jurassic Park (1993) were filmed in the open fields nearby.
At the end of the movie, Henry made a video for Lucy to let her know what had happened since the accident that caused her memory loss. In the video, Henry said on one card, "Red Sox win Series!" The next card read "Just kidding." The movie came out in February 2004. Later that year, the Red Sox actually broke an 86-year drought and won the World Series. Drew Barrymore was actually on the field after the win while filming scenes for Fever Pitch (2005).
Blake Clark, who is a Vietnam Veteran with the US Army, wears a hat from the USS Badger (DE 1071) named after Admiral Oscar C. Badger II, Charles J. Badger's son (1890-1958), was the first Navy officer to step ashore in Japan at the end of World War II and was also awarded the Naval Medal of Honor.
There are several references to the Hormel meat product Spam in the movie. According to Hormel, Hawaii leads the nation in per capita consumption of Spam. Over 6.7 million cans are sold annually in Hawaii, which equals 5.5 cans per year per Hawaiian.
While Henry, Ula, and all of his kids are golfing, Ula's kids run up to the golf ball to drive it. This is a trademark from Happy Gilmore (1996), another Adam Sandler movie. That's how he drives the ball.