Sometimes when I stand up after sitting or lying down I get dizzy and start to black out, though I have yet actually faint. Because my parents both have high blood pressure we have a machine for checking blood pressure. Whenever I almost faint after standing up, I check my blood pressure and it is usually around 90/55. It is normally around 110/65. Could this be orthostatic hypotension?

I am a 17 yo female who has been on prozac for the past 18 months due to panic attacks and ocd, though I have not had a panic attack on about a year. If I do have orthostatic hypotension could an SSRI such as prozac be the cause? What could other possible causes be? Is it something that I should worry about?