Go to sleep. What do you mean you're still awake?

Go to sleep. It's time for bed. I'm still sleeping.

Sleep: I haven't started to sleep yet. Go to sleep.

Not awake yet: I'm sleeping, but I'm not awake yet.

The meanings of the two are quite different.

For example, it's late, Xiao Ming hasn't slept yet, and his parents told Xiao Ming to go to bed early. I have to go to school the next morning, and I will be late soon, but Xiaoming hasn't woken up yet. I didn't even want to wake up.