A downhole motor has a bearing mandrel rotatably disposed within a housing, plus an impact adapter disposed above and connected to the bearing mandrel and rotatable therewith. The impact adapter has upwardly-projecting teeth engageable with downwardly-projecting teeth on a drive mandrel disposed above and coaxially aligned with the impact adapter. The drive mandrel is both rotatable and axially movable within the housing, and relative to the impact adapter. By means of a cam assembly and a helical spring (or other energy storage means) associated with the drive mandrel, rotation of the drive mandrel causes upward movement of the drive mandrel within the housing, thus compressing the spring. Further rotation causes instantaneous dropping of the drive mandrel, releasing energy stored in the spring, and causing the application of rotational and/or axial impacts to the bearing mandrel, and thus to a drill bit connected to the bearing mandrel.