Blood pressure varies throughout the day. In particular, it increases during exercise and decreases during sleep. Though hypertension can cause headaches, dizziness and visual disturbances, the majority of patients do not suffer from any symptoms. Hence the condition may remain undiagnosed. Having a routine blood pressure check is recommended or more comprehensively, a 24 hour ambulatory blood pressure monitor (ABPM) to give a more accurate picture of blood pressure levels and variation.