For the last month and a half I have been having a sensation of pressure in the centre of my chest, sometimes with the feeling of my heart beat, but mostly just the chest pressure. It happens when I am walking, standing, sometimes sitting. It is most frequent in the afternoon and evening. At first it would just be for a moment, but now is lasting for half an hour or longer. I am not particularly anxious about anything when this happens; do you think it is low blood pressure?