The phrase ‘run down’ is commonly used to describe a state of physical or mental exhaustion, where a person is in poor health or feels weak and tired.
For example:
• After working long hours without rest, she felt completely run down.
• He has been feeling run down lately due to stress and lack of sleep.
In addition to its meaning related to health, "run down" can also refer to something in a deteriorated condition, like a building or a vehicle, meaning it is in poor physical shape or no longer functioning well.
However, in the context of health, ‘run down’ specifically refers to being in poor health, feeling weak, or lacking energy.
Final Answer: to be in poor health