A police officer must have a legal reason to pull over a vehicle.  Being tired is not, in itself, is not a good enough reason.   If your car is being driven in an unsafe manner, the officer could pull you over.   For example, if an officer sees a car with a driver, who appears to be slumped over the wheel, has his eyes closed, has difficulty controlling the vehicle, or otherwise seems impaired, then the officer could pull that car over.   Extreme fatigue in a driver would look like driving under the influence to an officer, at least prior to the traffic stop.   Sleepiness can also mimic drug use, so an officer might ask you to submit to a blood test to determine if you are driving under the influence of drugs.

Fatigue can slow your reaction time down, making you less able to avoid collisions.   You should know that it is unsafe to drive when you are very tired.  Falling asleep at the wheel could cause you to have serious accidents.  It is far safer to be well-rested when you will be driving a car.  You have a legal responsibility to drive safely.