When a British-Iranian charity worker was abruptly released from a Tehran prison last week on a three-day leave and allowed to see her daughter, joy erupted among supporters in Britain, where her case has received extraordinary attention.

But when her request for an extension was denied, the elation turned to despair and anger. Then on Wednesday, the prisoner collapsed and was hospitalized over what her husband described as recurrent panic attacks.

The plight of the prisoner, Nazanin Zaghari-Ratcliffe, a 40-year-old representative of the Thomson Reuters Foundation who was arrested in Iran more than two years ago, is not unique. Critics of Iran’s opaque judicial system say foreign citizens — particularly Britons and Americans of Iranian descent — are often subject to capricious prosecution on vaguely defined political offenses.

Here are some questions and answers about Ms. Zaghari-Ratcliffe and some other high-profile foreign citizens known to be incarcerated in Iran.