Bad Night

I get my Rebif shots every other day. I try to stick with M,W &F. Friday night when I woke up to go to the bathroom. My legs quit on me. I couldn't even crawl. No pain or any feelings. Just dead weight. Thank God my husband is supportive enough to get up and do what ever it takes to help me. After I finally get back to the bed, when I wake up 3 hours later, I am okay to walk. I don't know why it happens. It has happened 4 times now. Any one out there with any suggestions or explanations?