Stop Ringing Ears

I have been to the ENT and have a MRI scheduled for tommorrow,but I want to hear from people with personal experience.

Yesterday, as i got up from my bed i got light-headed and i know it was from low blood pressure from getting up to fast (postural hypotension) but i also got a loud hissing sound (tinnitus) in my ear and i never ever have gotten this before when i get lightheaded i usually just get tunnel vision. Why did i get this hissing sound? How does low blood pressure effect the ears?