Depression is staggeringly common in the United States, with more than one in four adults reporting having been diagnosed with the condition in their lifetimes. In a given year, more than 8 percent of U.S. adults might report a major depressive episode. And there are more than 500,000 hospitalizations for a depressive disorder each year.

Representative Thomas Kean Jr., a Republican from New Jersey, announced on Tuesday that he had joined the ranks of those who had been hospitalized for depression.

Mr. Kean, 57, said that over the past few months he had come to understand “how long depression had been affecting my life.” During a speech on the House floor in Washington, he provided no details of his treatment.

Some people develop depression for the first time in middle age or older, but the usual age of onset is younger, said Dr. Mark Rapaport, the president of the American Psychiatric Association.

“I’m grateful that the congressperson is able to be forthcoming because this is a treatable disease of the brain, and we need people to know that,” Dr. Rapaport said.

A Safe Environment

Experts cited several reasons why someone might be hospitalized for depression, the most common being if the patient is experiencing thoughts of suicide or self-harm.

“Being in the hospital ensures that somebody is being monitored around the clock, and they’re in a safe environment to keep them protected while we begin treatment for depression,” said Dr. Jonathan Komisar, an assistant professor of psychiatry and behavioral sciences at Duke University.

That safe environment can also offer protection for people who may have stopped caring for themselves — patients who are unable to get out of bed, eat or drink, bathe or perform other necessary daily tasks.

“Folks don’t get hospitalized unless their depression is truly very, very severe,” Dr. Rapaport said.

Thorough Diagnostic Evaluation

Another reason someone might be hospitalized for a mental illness is for a more thorough diagnostic evaluation, said Dr. Gerard Sanacora, a professor of psychiatry at Yale School of Medicine.

Symptoms of depression can include sadness or low mood, feelings of worthlessness or guilt, or a loss of interest in things someone used to enjoy. But they can also involve more physical symptoms, such as slowed movements and changes in appetite or sleep, and cognitive issues, like brain fog or difficulty making decisions.

These symptoms can be “central to many other different disorders and pathologies,” Dr. Sanacora said. As a result, clinicians have to rule out other potential diagnoses — such as neurodegenerative disorders or other psychiatric disorders — to ensure that depression is the right cause. “Depression is what we call a diagnosis of exclusion,” Dr. Sanacora added.

In his brief address, Mr. Kean described his illness in somewhat vague terms. “When people hear the word ‘depression,’ many people think it simply means feeling sad,” he said. “But depression is so much more than that: It is physical, it is emotional, and until you experience it yourself, it is difficult to fully understand how powerful this illness can be.”

Expedited Treatment

An inpatient setting can allow “for more expedited care,” Dr. Komisar said. “It’s much easier to adjust medications rapidly when you have 24-hour monitoring.”

There are several treatment options for people hospitalized with depression. The “most common and conventional” is the use of antidepressant medications, which can be effective for some people, but not for others, said Dr. Leonardo Lopez, who is vice chair for inpatient psychiatric services at NewYork-Presbyterian. And it can take a month or two for the medications to work.

Another treatment is transcranial magnetic stimulation, which directs magnetic pulses to stimulate brain circuitry, although it is less commonly used in hospital settings.

Some patients with depression are treated with ketamine, which is effective at reducing suicidal thoughts quickly, Dr. Lopez said.

Another treatment option is electroconvulsive therapy, or ECT, which involves applying an electrical current to the brain, causing a seizure.

“This is the most effective treatment we have for treatment-resistant depression,” said Dr. Lopez, who oversees ketamine and electroconvulsive treatments across much of the NewYork-Presbyterian Hospital system. “We will often utilize that in cases of depression that are very severe, and we feel like we need to go to the most effective thing quickly.”

The decision about which treatment to try depends on several factors. If it is a patient’s first hospitalization for depression, the tendency would be to try antidepressants before moving to electroconvulsive therapy, which requires general anesthesia, said Dr. Lopez.

“On the other hand, if the patient is severely suicidal or has lost 40 pounds because they have not been eating for months,” ECT might be appropriate to try right away, Dr. Lopez said.

Duration of Hospitalization

In his remarks, Mr. Kean said that he had thought he would be gone for just a few weeks, but he ended up being absent for several months.

Experts said that people may be hospitalized for a few weeks to a few months. “It depends on the severity of their depression. It depends on their support system outside of the hospital. It depends on the treatments that we are choosing to use,” Dr. Komisar said. Key signs that someone is ready to be discharged are that their symptoms have improved and they will be safe living at home, he added.

Returning to normal daily activities, such as going back to work, can take several more weeks or months, Dr. Sanacora said. The goal, he added, is “to get people back to their previous level of function without overwhelming them immediately.”

Although recovery from a severe depressive episode can be a lengthy process, the experts stressed that the most important thing is seeking treatment.

“I see many patients that have very high-level jobs, and it is kind of sad to know that people are afraid, ashamed and really discouraged from getting treatment,” Dr. Sanacora said. “There’s almost more support for continuing to work in an impaired state than there is for getting the appropriate help that will allow people to return to their high level of function.”