Hello Lisa, nice to meet you - I'm Amy. I was diagnosed R&R MS in June 2019 - I was 32, now 33, i've been taking Tysabri for over a year now, taking it every 4 weeks - the first 3-4 were exhausting but my body seemed to adapt each time I had the infusion it was less tiring, to the point on my 5th I was able to independently get to and from my infusion alone and I was barely tired. I have never experienced feeling off balance. On my 13th infusion in June 2020 I was told I would be moved to Tysabri every 6 weeks - great - less chance of PML risk, less trips per year, my first infusion at 6 weeks tired me a lot but still no where near to what it did back in June 2019, I think my body just needs to adjust again to it's new schedule. I started weight lifting in summer 2019 and consciously eat healthy, daily yoga and hourly walk. I can honestly say I have not experienced any MS issues on Tysabri. I wonder if environmental issues are playing a part causing your off balance- heat/anxiety (CV19)/stress/fatigue/sugar - in any event (as I'm sure you will anyway) I'd recommend sharing the change you noticed with nurse at your next infusion if you have this off balance for more than 48 hours call the MS helpline to seek guidance. Really hope this helps somehow xo