A four-line letter, signed by the attending physician of Congress and released by Senator Mitch McConnell on Thursday, suggested that his recent spells of speechlessness were linked to “occasional lightheadedness” perhaps brought on by his recovery from a concussion last winter or “dehydration.”

But seven neurologists, relying on what they described as unusually revealing video of Mr. McConnell freezing up in public twice recently, said in interviews Thursday and Friday that the episodes captured in real time likely pointed to more serious medical problems afflicting the longtime Republican leader.

Some of the neurologists, while cautioning that they could not diagnose the minority leader from afar, said that the letter and other comments from Mr. McConnell’s office appeared to fall short of explaining why he abruptly stopped speaking during news conferences in late July and again on Wednesday.

“If I gave that tape to a medical student and that was his explanation, I’d fail him,” said Dr. Orrin Devinsky, a professor of neurology at the NYU Grossman School of Medicine, referring to the account given by the attending physician of Congress on Thursday. “Medically, these episodes need to be taken seriously.”

The neurologists said that the episodes justified close medical attention and could prompt treatment to keep them from recurring. While several possibilities were suggested, including mini-strokes, doctors said that the spells appeared most consistent with focal seizures, which are electrical surges in one region of the brain.

The senator’s aides have not revealed what type of follow-up care Mr. McConnell may be receiving. Doug Andres, a spokesman for the senator, said on Friday he had nothing to add beyond the letter by the Congressional physician, Dr. Brian P. Monahan.

More details about the medical history of Mr. McConnell, 81, including whether he has been having such episodes off camera, would also help rule out other possible explanations for the spells, neurologists said.

Whether caused by seizures or mini-strokes or something else, spells like Mr. McConnell’s would not preclude most patients from working or socializing normally, doctors said.

“Seizures have a stigma in our society, and that’s unfortunate because these are very brief electrical interruptions in behavior,” said Dr. Jeffrey Saver, a professor of neurology at U.C.L.A. “Between those rare episodes, which are usually well controlled with medicines, people function perfectly normally.”

Still, experts said that seizures carried some elevated risk of cognitive or behavioral problems and could affect older patients differently.

Rarely does the public get as complete a glimpse of a serious medical event in a public figure as it did twice in recent weeks with Mr. McConnell. For neurologists, videos like those showing Mr. McConnell from the moment he appeared to lose the ability to speak are far more than mere curiosities.

They can help form the basis of a diagnosis, as homemade videos of everyday patients occasionally do in standard neurology practices.

“They’re very helpful, because you’re not subject to the vagaries of someone’s description and you can capture the beginning of it, which is important especially for seizures,” said Dr. Anthony Kim, a professor of neurology at the University of California, San Francisco.

Details as small as the direction in which people’s eyes are pointed during such an episode offer potential clues about the cause, Dr. Kim said.

After watching Mr. McConnell’s symptoms play out — his abrupt stop in speech, his eyes fixed in the distance, his seeming recovery after about 30 seconds — Dr. Kim said that “the possibility at the top of my list would be a seizure.”

That Mr. McConnell’s second spell so closely mirrored the first pointed even more strongly to a seizure, neurologists said.

Mini-strokes, which result from a clot that reduces blood flow to the brain, can also cause brief periods of impaired speech. But they rarely produce the same constellation of symptoms each time they recur, given that clots are unlikely to travel at random to the same part of the brain twice.

Focal seizures, on the other hand, are often triggered by an irregularity in one specific part of the brain, creating what doctors refer to as stereotypic symptoms. They are known to stop patients dead in their tracks, seeming to cut them off from their surroundings.

Patients can often respond reflexively to questions during such an episode — as Mr. McConnell did on Wednesday, saying “yeah” when asked if he had heard a reporter’s question — even if they appear unable to voice their thoughts or engage with their environment.

Mr. McConnell suffered a concussion in March, a risk factor for seizures. The seizures can be caused by a bleed in the brain or a scar from a traumatic head injury. Previous strokes or other kinds of damage to brain tissue can also lead to seizures in older people, who as a group experience the onset of seizures almost as often as children do.

Some seizures are provoked by triggers like abnormal blood sugar levels. But if someone has had two seizures that cannot be explained in that way, neurologists said that would typically be enough for a diagnosis of epilepsy, a common neurological disorder affecting more than three million Americans that can arise at any age. They would generally prescribe anti-seizure medication.

“Two seizures you definitely would want to treat,” said Dr. Sami Khella, the chief of neurology at Penn Presbyterian Medical Center. “You don’t want them to happen — they’re not good for you.”

Many patients function completely normally and show normal brain wave activity between seizures, allowing them to remain active and working even as they are forced to forgo activities like driving.

But they do cause patients to miss periods of time during episodes. A seizure at an inopportune moment, like when crossing the street, can be dangerous. And focal seizures involving one region of the brain can generalize, causing episodes characterized by jerking movements or epileptic spasms.

Beyond that, one or two seizures can beget more, a cycle that neurologists try to interrupt with treatment. “The more the brain seizes, the more it learns to seize,” Dr. Khella said.

Other complications can follow. A phenomenon known as sudden, unexpected death in epilepsy kills an estimated one in 1,000 people with epilepsy each year.

“If you do get epilepsy as an elderly individual, there are concerns about things like memory, about cognitive function, because your resilience at 80 is going to be far less than when you’re 20 or 30,” said Dr. Devinsky, who directs NYU Langone’s Comprehensive Epilepsy Center.

Neurologists said they could not rule out other possible explanations for Mr. McConnell’s episodes.

Dr. Gavin Britz, a neurosurgeon at Houston Methodist, said he would want to exclude Parkinson’s disease, which can also cause freezing episodes.

But neurologists agreed that suggestions that Mr. McConnell was merely lightheaded, while possible, were difficult to square with the video. Dehydration could exacerbate other conditions, they said, but such patients would be unlikely to stay upright or recover so quickly without fluids, as Mr. McConnell appeared to do.

“We don’t have 100 percent information, so we’re kind of in the dark,” Dr. Devinsky said. “But we do have this very powerful clinical information, which is quite honestly how I have to diagnose seizures and epilepsy all the time, often without the video.”