Usage note
“忽然”用来表示事情突然发生,比如突然下雨或者突然想起某件事。
hūrán lái yòng biǎoshì shìqíng tūrán fāshēng, rúkě tūrán xiàyǔ huòzhě tūrán qǐxīng mǒu jiànɡè.
"忽然" is used to indicate that something happens suddenly, such as suddenly raining or suddenly remembering something.