Quick answer
Get medical care and preserve the condition and location; responsibility requires facts beyond the fact that a fall occurred.
Do now
If safe, photograph the hazard, surrounding area, lighting, signs, and footwear. Record witnesses and report the incident accurately. Identify the owner, occupier, and any public connection. Ask promptly about camera-record preservation.
Watch for
A store report is not a lawsuit or government notice. Sidewalk responsibility and notice requirements can be highly local.
Official sources
NJ Courts — Statute of Limitations FAQ, NY Courts — Statute of Limitations Timetable, DC Code § 12-301, NJ Treasury — Tort and Contract Notice, NY Legislature — General Municipal Law § 50-e, DC Code § 12-309.