Good question. The simple answer is that there isn’t a simple answer. It always depends on the situation. Getting out of the shower in your hotel room and slipping on wet tile is different than slipping on water that has pooled in front of a soda machine at a fast food restaurant. Your best bet for knowing whether you have a case or not is to consult a slip-and-fall attorney.
You don’t have to, but it’s best to make records of things while they’re fresh in your mind. If you fall at a business (say a grocery store), it’s not unusual for the business to have a policy of filling out a report at the time of the event. This can be a good thing. If a report is compiled, make sure you get your own copy of it. Don’t feel obligated to sign any documents or make binding statements. It’s not in your best interest to do so. The report is your chance to gather evidence, record the exact details of the event, and gather witness testimony and contact info. If the fall happened at a private residence, you will want to make notes for yourself while events are fresh in your memory.