Hypertension is one of the most common diseases in industrialized countries. It is estimated that about 12 million people in Italy suffer from hypertension, but that of these only 70% has been diagnosed and is following treatment. 

As a general rule, we are said to have "high blood pressure" or to suffer from hypertension when our "systolic" pressure values (or "maximum" that corresponds to the moment when the heart contracts and pumps blood into the vessels) are equal to or greater than 140 mmHg and when our so-called "diastolic" pressure values (or minimum, which corresponds to the time when the heart expands to fill up) are equal to or greater than 90 mmHg.       
These are general values (measured by your doctor or pharmacist) which, of course, must be accessed depending the individual and evaluated in conjunction with other elements. As a matter of fact, there are risk factors such as old age, diabetes or obesity, and risky behaviors, such as smoking or alcohol consumption that can alter blood pressure control mechanisms causing blood pressure to increase.
External factors may also affect blood pressure, often lowering it, for example, during heat waves especially when combined with air pollution conditions, as often happens during summer in big cities.  In this regard, it can be helpful to visit the website of the Ministry of Health, which lists ways in which to tackle the summer wisely and prevent health risks. In particular, it highlights that people who regularly take certain medications for high blood pressure or cardiovascular disease are at risk of disorders caused by excessive heat. Therefore, it is recommended that these people measure their blood pressure regularly and consult their family doctor to make any necessary changes in treatment or if they experience any discomfort, however slight.
(link to  http://www.salute.gov.it/dettaglio/phPrimoPianoNew.jsp?id=321)
Another good habit, to acquire through a change of mindset that considers prevention and health as daily habits and not just reactions to perceived malaise, is to check the blood pressure regularly and independently using a blood pressure monitor.
Research has led to the extreme accuracy of these devices, certified by the presence of the label attesting their ESH Clinical Validation and by the ability to verify calibration in pharmacies that offer this service.  A high level of customization is added to this, which ranges - for example - from very simple devices designed with the elderly in mind, to extra-large displays for those with vision problems (elderly people but also diabetics), to wrist models designed for obese people, etc..as well as devices with more sophisticated features such as exceeded threshold value alerts and - when the unit is equipped with a memory - the ability of the blood pressure monitor to communicate your computer and send results to your doctor via e-mail.