my differential diagnosis is it can be a syncopal attack or
presyncope.
Syncope, is defined as a short
loss of consciousness and muscle strength, characterized by a fast onset, short duration, and spontaneous recovery. It is due to a decrease in blood flow to the entire brain usually from low blood pressure.
autoimmune diseses canalso lead to blocking of
carotid artery a artery which carry blood to brain
so i would advice you to go for
carotid artery doppler
2d echocardiography(to find
ejection fraction of heart,as bp is maintained by amount of blood pumped out of heart in each contraction)
Head up tilt test
basically once you rule out the cause of your low blood pressre ...youcan treat it
keep
mri on hold for the time being
and get the test done which i have advised as a initial work up
if everything is normal in all these tests then go for mri brain