First Tysabri infusion and fatigue

Hello, I have started Tysabri on Friday last week after being on Copaxone for 5 months. I did not really feel any different after that until yesterday at work when I suddenly got really tired. It was so bad that I slept on the floor for more than an hour :frowning: and was sent home.

I have expecting to feel the side effects on the day or at least the day after but it happened 5 days post Tysabri. Is did normal or it has nothing to do with the infusion?