Re: orthostatic hypotension fainting\passing out
Yes, orthostatic hypotension can cause fainting.
I'm guessing you are fairly young (and healthy). There are medications that can cause the problem. Anemia is another one. That would be more likely in a vegetarian. If neither of these apply, it could be as simple as not drinking enough water during the day. Dehydration can affect blood volume which can lead to OH.
If the problem persists, see your doctor.