Re: Passing out!
One of my Grand Daughters had all of the symptoms you describe.
Finally diagnosed as POTS syndrome.
You might want to have a look at it?
"Postural orthostatic tachycardia syndrome (POTS) is a condition in which a change from lying to standing causes an abnormally large increase in heart rate. This occurs with symptoms that may include lightheadedness, trouble thinking, blurry vision, or weakness. ... The cause of POTS is poorly understood."
She is now on medication and doing well.