In reality, there is no ”sleeping" hair - this is an advertising move.
Just as there are no sleeping teeth and nails. Everyone has a certain number of hair follicles that form hair. According to them, trichologists determine whether it is possible to restore the volume of hair or not.
It is possible to increase the density of hair with stimulating drugs and procedures, but this is in the presence of bulbs. If they have started to be replaced by connective tissue, then simple methods will no longer help.
In fact, the volume is initially determined genetically, and it does not happen that part of the hair has been sleeping all its life. But damaged bulbs can be restored.