I have been getting head rushes a lot for the past 6 months.?

Just about 10 min ago got up from the computer to get my dogs from outside and got a really bad head rush couldn't see at all. I held on to the side of the door and started shaking. I don't how bad because i couldn't see. And about 2 months ago i got up from the breakfast table and was walking down the hallway got a head rush and fell, but i don't remember falling. I have taken many blood test, and was given and MRI. Nothing showed up. But after the insistent that just happened my hands are still a little bit shaky. I don't know if this is because I'm scared or what.