What Causes Fatigue Along With Dizziness And Numbness In Toes?

I have episodes of extreme fatigue, dizziness, numbness in my toes and tingling all over my body. I have suffered from these attacks for about five years and they hit me about twice a year, lasting from 2-6 weeks. The tingling is a new symptom that just began with the latest attack. I have an appointment for an MRI as all the bloodwork has been normal, but I have to wait until May. What is this?