When I don't get enough sleep, my eyes struggle to stay open especially inside. I typically struggle to stay awake in class if I have not had lots of sleep. I try my best to pay attention but will often find myself microsleeping. My body also feels more sore and less "explosive" doing physical activity such as working out or playing sports. My reaction time is definitely slower, and I also do not talk as much when I do not get enough sleep.
An example is one time when I was 15, I spent the night with a group of friends, and we stayed up until about 6 AM. It was not smart of me mainly because I had a soccer game at 11 AM the next day. I was so sleep deprived that I found myself closing my eyes just by sitting on the bench before the game. I was very slow and did not perform well at all. I definitely learned a lesson that day.