(CNN) -- It was either mind-blowing or completely forgettable. Either way, Alice doesn't remember.
One August morning, Alice and her husband, Scott, had sex.
That's when things became confusing. Rather than appearing pleased, Alice, 59, seemed disoriented.
As they lay in bed, Scott (the couple asked that their last name not be used) flicked on the television, which was showing the Olympics. This perplexed Alice. "Is there an Olympics?" she asked. This was during the Michael Phelps mania, when the swimmer seemed to be everywhere.
"Are you sure there is an Olympics?" Alice asked again.
Scott recalled, "I saw that something was wrong, so I asked her, 'OK what day is it?' "
Alice appeared even more perplexed.
"Who's our president?" he quizzed.
"Bill Clinton," she answered. This was 2008.
Scott darted out of bed and called 911. The paramedics suspected a stroke and rushed the befuddled Alice to the emergency room.
For decades, doctors described cases of a rare neurological condition that usually occurred in patients over age 50. Neurologists noted that patients knew their identities, but couldn't retain recent memory, where they were and how they got there. They showed no other symptoms.
Sex is one of the major triggers for the baffling medical condition called transient global amnesia in which patients lose their ability to retain immediate memory.
TGA usually occurs after the person engages in strenuous activity -- such as having sex, vigorously exercising, suddenly immersing into icy or hot water, straining to dig a stuck car or even bumping the head.
"The unifying thing about each of them is they produce a sudden and significant change in blood flow," said Dr. Louis Caplan, professor of neurology at Harvard Medical School.
Alice arrived at the hospital around 8 a.m. in seemingly perfect health. As medical staff poked and prodded, Alice cheerfully peppered them and her husband with questions.
"Where am I?" she asked.
"You're in the ER," Scott answered.
"How did I get here?"
"The ambulance brought you here," he replied.
"Wow." Alice paused for about 10 minutes, observing the hubbub at the hospital before she repeated her initial questions. At some point, she started asking different ones.
"What was I doing before this? How did I wind up here?" she inquired.
Scott told her.
"So we were..."
"Yeah," Scott answered.
"Then this happened?"
"Let me get this straight. We had sex. I wind up in the hospital and I can't remember anything?" Alice said. There was a slight pause.
"You owe me a 30-carat diamond!" Alice quipped, laughing. Within minutes, she repeated the same questions in order, delivering the punch line in the exact tone and inflection. It was always a 30-carat diamond.
"It was like a script or a tape," Scott said. "On the one hand, it was very funny. We were hysterical. It was scary as all hell."
While doctors tried to determine what ailed Alice, Scott and other grim-faced relatives and friends gathered at the hospital. Surrounded by anxious loved ones, Alice blithely cracked jokes (the same ones) for hours.
"Let me get this straight," Alice said to her husband. "We had sex. I wind up in the hospital and I can't remember anything? Was it good for you? 'Cuz it wasn't good for me because I couldn't remember anything."
"That's the closest I came in my life to being hysterical," Scott said. "You're literally laughing and crying at the same time."
Hours later, the doctors made the diagnosis. And figured out the cause.
"This is actually a well-known precipitator. One of the things people have done to look at transient global amnesia is to look at frequency of various precipitants and sex always comes out as one of the most common," said Caplan, a leading stroke expert at the Beth Israel Deaconess Medical Center in Boston, Massachusetts, who was not associated with Alice's care.
"It usually is after climax that it develops," he said about its onset.
Patients who have a history of migraines and headaches are more likely to get TGA as some people report getting terrible head pains related to orgasms, called coital headaches.
"I remember the previous night going to sleep with a subtle headache and not taking anything for it," Alice recalled. "And apparently, the next morning, my husband and I had intercourse. From what I found out, there was an orgasm."
In 1999, Johns Hopkins University doctors described two patients in their 70s who suffered TGA after having sex. In these cases, the act of "bearing down" -- which occurs when people move their bowels, give birth or have sex -- created pressure in the brain's blood vessels, resulting in temporary lack of blood flow that caused amnesia, according to the study published in The Lancet.
Levitra, which is a pill for erectile dysfunction, lists TGA as a possible adverse reaction.
Caplan likened the hippocampus, which is responsible for short-term memory in the brain, to a tape recorder. If blood flow to the brain gets restricted, the hippocampus cannot record new memory.
"The hippocampus is responsible for initially recording the information so you can play it back," he said. "So if it's not working, you won't get the information."
TGA usually occurs once, but in some cases, it could become recurrent. Studies that took advanced brain imaging of patients experiencing TGA showed abnormalities in the cerebral arteries in the left hippocampus of some, Caplan said.
"It's not enough of a stimulus or deprivation that it permanently injures the brain. The brain recovers," he said. "There should be no deficit other than memory and it should be brief."
As the day progressed, Alice's repetitive questions came every 10 minutes, every 15, then 30, until she regained her immediate memory. Around 2:30 p.m. that day, Alice remembers sitting on a hospital bed and seeing her husband looking upset.
Although Alice recovered fully, she still cannot remember what happened that morning. The last thing she remembered was going to bed the night before with a slight pain in the right, rear area of her head.
"I was lucky because nothing bad came of it," said Alice, now 60. "I wasn't frightened. My husband and family were frightened. I was totally out to lunch."
One consequence from the amnesia was that it provided her two grown children with too much information about their parents' sex life.
A year after her episode, Alice said the amnesia had not deterred her sex life, but she avoids having intercourse when she has a headache. She tells her husband, "So sorry, you can wait."
And Alice has yet to receive a 30-carat diamond for all her troubles.