Higher notes require higher support energy. A higher volume also requires a higher support value. The support values for pitch and volume must be multiplied. If a singer has to sing an ascending scale at volume 5, the support values for each individual note will be for example: 1, 2, 4, 8, 16 and so on. If the singer instead chooses volume 10, the support values will be 5 times higher: 5, 10, 20, 40, 80 and so on.
In the lower part of the middle of the voice, where you are speaking, support values are not so high and multiplying these low values by 5 seldom presents a problem. When you sing in the higher part of the voice (or the very low part of the voice), the support values quickly become enormously high when multiplied by 5, and it becomes difficult to apply enough support energy. Somewhere on this scale a singer might suddenly run out of support energy and the voice will change to a vocal mode or density that requires less support energy in that area of the voice. As a result the voice may break from one vocal mode or density to another and the volume changes abruptly, for example from volume 10 to volume 2.