You couls be low on iron in your blood. I had to take iron tablets when i wqw younger because ibwas always tired
It could be a Thyroid issue. You should get it checked out.
u could be pregant or something else u need to go talk to the doctor
Dysautonomia, hypotension, hypoglycemia, concussion, vascular compression, renal disease, hormonal imbalance, electrolyte imbalance; and many other conditions can cause those symptoms. If they are recurring or persistent symptoms you need to be evaluated by a doctor.