From your history, it appears that you had developed a scalp hematoma following the fall. Relatively fresh scalp hematomas, on palpation, often feel as though the skull bone itself is depressed. Such "true" depressions of the cranial vault do occur in newborns and infants("pond fractures") as their bones are very thin.
Scalp hematomas (like hematomas elsewhere in the body), organize and then gradually disappear. Small hematomas would generally be expected to have resolved by 6 weeks.Perhaps it was somewhat larger in your case. If there is any associated headache or vomiting, one must report to the doctor urgently. In any case, it may not be a bad idea to visit your family doctor for an assessment.
MB BS, MS, FRCS(Edinburgh)