✔ 最佳答案
I write to apply for *(a certain period of) no-paid leaves. Recently, I always lose my sleep at nights due to heavy workload and academic pressure. It really bothers my physical and emotional normal functionings, thus I do believe I could no longer fulfill my working duties temporarily. I apologize for any inconvenience caused.
I look forward to receiving your reply as soon as possible.
注: *(xxx) 表示 以期效代替, 如: 3 week no-paid leaves 等等