Hello Marvil,yep I've had that one,was it a sensation like you were unsteady and were going to fall over along with 'something bad'was going to happen?I found that I felt kind of exposed in open spaces i.e. crossing bridges or walking across a big field, I read that this could be due to feeling like there was no hiding place if you needed to escape quickly.Escape from what though?For me I was trying to escape from the panicky feelings that I had inside, which my brain was telling me was due to the open space,when really it was'nt.It was my anxiety disorder trying to rationalise that fear =open spaces.
After taking it slowly and building up my confidence bit by bit it began to disappear as I hope it will for you too. Good luck... Neil.