"feeling sleepy" is correct and usable in written English.
You could use it when you want to indicate that you are tired and preparing to go to sleep. For example: After a long day, I'm feeling sleepy, so I'm going to get ready for bed.
(That's if you need research to tell you that sleep makes you feel better when you're feeling sleepy).
The most obvious is sleepiness; not sleeping enough leads to feeling sleepy and a strong desire for sleep.
Of those with more frequent/severe daytime sleepiness (n = 202), 95 (47%) reported feeling sleepy in the morning at least three days per week, 103 (51%) reported feeling sleepy during daytime at least three days per week, and 94 (47%) reported having had naps at least three days per week.
The next-day-sleepiness item also used a rating ranging from 0 suggesting not feeling sleepy due to prior night's sleep pattern to 10 for feeling extremely sleepy.
Right away I'm feeling sleepy.
I recall riding on the open prairies feeling sleepy but never unsafe.
Although any type of light stops you feeling sleepy, light towards the blue end of the spectrum is especially potent.
"I can see that you all are feeling sleepy after that lunch," he said with a smile.
It happened so fast that I doubted myself in the very moment of wonder, and, feeling sleepy and uncertain, decided not to mention it to anybody.
Later, after I realized that none of us were feeling sleepy, they started talking about children, and their voices made my heart recoil.
"Not getting enough sleep is probably the most common problem," he said, "We know from experience that feeling sleepy isn't enough to get people to get more sleep".
