To become unwell; to have one's physical condition deteriorate (e.g., catching a cold, becoming fatigued, or otherwise feeling sick).
最近忙しくて寝不足が続き、ついに体調を崩してしまった。
I've been busy and sleep-deprived lately, and I finally became unwell.
旅行中に食べ物が合わず、彼は体調を崩してホテルで休んだ。
While traveling his food didn't agree with him, so he fell ill and rested in the hotel.
無理をすると体調を崩すので、適度に休むことが大切だ。
If you overdo it you'll get sick, so it's important to rest appropriately.
彼女は体調を崩したため、会議を欠席した。
She missed the meeting because she fell ill.