Always get medical help if you have any doubts about whether it's a stroke or MS. It takes experience to learn how to tell the conditions apart. Even then, it may not be clear. Given how serious a stroke can be, you're better safe than sorry.
If it is a stroke, you don't have time to wait. Quick treatment can save your life and help prevent long-term problems. If it turns out to just be an MS relapse, that's important for your doctor to know, too. It could be a sign to make some changes in how you manage your MS.
One of the best things you can do is talk to your doctor about your chances of having a stroke. If you have problems like diabetes, heart disease, high blood pressure, or high cholesterol, your risk is higher. Your doctor can help you get those under control.