If you’ve ever woken up in the morning feeling groggy (昏昏沉沉的) or absent-minded, you’ve experienced what’s called “sleep inertia (迟钝)”, which can be a problem. “If you don’t wake properly, your work performance can be degraded (退步) for periods up to four hours, and that has been linked to major accidents,” said Stuart McFarlane, a scientist at the Royal Melbourne Institute of Technology, Australia.