Instead of just letting themselves drift off into dreamland, they kept on checking to see if they were still awake, and that quick mental check woke them up.
dict.youdao.com
有些晚上，我会难以入眠，但今晚，我却不用数羊了。
Some nights I have trouble falling asleep, but tonight, I didn't need to count any sheep.
www.kekenet.com
问题还没解决时，不要上床睡觉，因为这些问题会使你难以入眠。
You should not take problems to bed with you, for they make very poor bedfellows .
