在英文中，形容一个人睡不着觉的常用表达是 "have trouble sleeping" 或 "have insomnia."
"Have trouble sleeping" 是指一个人在尝试入睡时会遇到困难或者难以入眠。例如：
I always have trouble sleeping when I'm stressed out. (我在压力大的时候总是睡不着觉。)
He has trouble sleeping because he works night shifts. (他因为上夜班而睡不着觉。)
"Have insomnia" 则是指一个人患有失眠症，即持续性地睡不着觉或者入睡困难的病症。例如：
She has been suffering from insomnia for years. (她多年来一直患有失眠症。)
He was diagnosed with insomnia after experiencing difficulty sleeping for several months. (在几个月来睡眠困难后，他被诊断出患有失眠症。)
两个表达的区别在于 "have trouble sleeping" 是指临时性的睡眠困难，而 "have insomnia" 则是指长期性的睡眠困难。