Witnesses are important but not necessary. You may have had people come to your attention after your accident or fall. They have not witnessed the accident but the aftermath of the accident and may be asked to give their account of what happened afterwards only. Your accident may have been caught on CCTV and this the best form of evidence of your accident and the mechanics of it. You can also take photographs of the spot you fell at to assist in investigations.
No one saw me falling, will this be a problem?