If the problem is still with you in the morning, then you can seek proper medical care at a doctor's office, clinic or pharmacy. Your first aid kit should take a small corner of your carry-on bag. Take small containers and pack spillable items in zip-lock bags. If you plan to do a lot of walking, and most tourists do a lot of walking, pack sensible shoes. Break them in before leaving home.
Many people ask about sneakers in the city.
If you are an adult, white sneakers in Europe will brand you as a tourist. Well, not really, since you really are a tourist, but it does attract the attention of pickpockets who target tourists. It's better to blend in with the crowd. You can find comfortable dark-colored suede or leather shoes that should suit your needs perfectly. If you are young enough in age or spirit to travel with your belongings in a backpack and sleep in hostels and city parks, then jeans and sneakers are fine.