The condition you are describing is 'White coat hypertension'.
In this condition, blood pressure of patient often goes up in hospital setting and normalizes at home. One of the reason for tachycardia
To know if you have real hypertension or not; get blood pressure recorded at least on 3 intervals, when you are not stressed.
Avoid taking coffee/tea before blood pressure recording.
Causes for hypertension in young patients is usually renal diseases, cardiovascular causes [Coarctation of the aorta], endocrine disorders.
Take simple steps to avoid hypertension.
1] Reduce dietary salt intake.
2] Regular exercise, weight reduction.
3] Eat healthy diet rich in fruits, sprouts,vegetables.
4] Moderation of alcohol consumption.
5] Treatment of underlying cause.