Here's the answer:
“正准备睡呢”
(zhèng zhǔn-bèi shuì ne)
Watch a real native speaker say it:
Here's how it sounds in a textbook:
You could also say:
- wǒ zhèng zhǔn-bèi shuì ne
Fun fact: the hundreds of thousands of people learning Chinese with Memrise get this phrase correct 90.05% of the time!