I was recently put on medications for high blood pressure. My blood pressure is 137/78. However, for the last couple of days, when I stand up I almost pass out. When I sit down it goes away. When I was in the ER before, they told me that my blood pressure drops when I stand up. I had to leave work today ,because I need to stand for my job, and I was too light headed to stay. I took my blood pressure and it was 137/74. Then I stood up and took it again. It was 93/62. What causes this?