Trust me not. The two black nuts you refer to are lock nuts. Inside them you should see two washers and then the 'bearing cones', they will have two flats with the rest being round. It sounds like your two black nuts have loosened followed by the cones. You need to re-tighten the cones, whilst checking that the bearings do not bind, and then re-tighten the lock nuts to fix things in place. Two spanners are recommended. One holds the cone at its set position and the other tightens the lock nut. You might take this opportunity to take it to bits, clean it and put some new grease in.

Someone with more experience may be along soon.