Shedding
Shedding is a normal part of the hair cycle and for a normal scalp nothing to be concerned about. Every persons scalp hair is shed regardless if they have male pattern baldness or not. Hair follicles do not die during the telogen resting phase but are just inactive waiting to start the next growth cycle.
An extreme case of shedding
Many men report increased shedding as a side effect of a hair loss treatment program. But others report no increase of shedding and still others report massive sheds.
It is important that you not panic during this time and remain on your treatment program. Your body will adjust to the hormonal changes and the hair cycle will return to normal.
Some topical's such as minoxidil will also cause shedding as the follicles cycles are reset. If you continue to use minoidil the follicle will produce larger and larger hair. The shedding is a good sign that the topical is working.
Large sheds happen when hairs get synchronized into more uniform cycles as can happen when taking certain hair loss drugs such as Finasteride. This synchronization will force more hairs into the telogen phase at the same time and you will see more hairs shed at the same time. Big sheds will become less and less frequent the longer you are on the drug as the cycles become more random again.
Remember that shedding is normally a good sign because a new stronger hair shaft is to follow. There may be periods where your overall hair will look thin but as the new hair shafts come in they will be thicker and healthier.