Call your doctor. If no response go to ER.
Hi and welcome to our little MS community,
With out knowing any of your situation, it's hard to know if this is a medical emergency or another MS attack!
If you can usually walk or climb your stairs, and even though you are using your wheelchair more your legs usually hold your body weight...... it's possibly a relapse but unless it's continued or worsened for longer than 24/48 hours, it's also possible that you really over did it yesterday and today your paying the price of fatigue and or muscle weakness, more a pseudo relapse than a genuine one and if it is a pseudo your expected to improve with rest......
It's going midnight over my side of the world but if it's day over your side, i'd first try contacting your neuro or call the clinic you had your infusion and explain what's happened.....otherwise if it's after hours and you don't have a doctor/nurse on call service to get advice, you really might need to head to the ER if your really worried.
Sorry I couldn't be of more help!
PS let us know how you get on
If this is a major symptom progression, and you live on your own, YES! Get to an ER and get checked out. I would also contact your neuro and get him/her in the loop.