生病 (shēng bìng) is a separable verb meaning 'to fall ill, to get sick'. Unlike 病 (bìng), which can be a noun ('illness') or a verb ('to be ill'), 生病 always refers to the process of becoming sick and can be split (e.g., 生过病 'have been sick'). It is the standard way to say 'get sick' in everyday speech.