When the VA reviews your application, they look for proof that your hypertension started when you were on active duty. Or, that you had existing hypertension that worsened during your active duty.
Most people with hypertension, including veterans, do not experience any symptoms. The only way to confirm that you have hypertension is to have your blood pressure checked.
Some veterans will experience secondary hypertension, which means their hypertension is caused by another service-connected illness or injury.