For some people red line behavior indicates changes in the play style. So I would follow your red line and see if it start to go in different rate than before to get hints when session is too long. Obviously green line is good indicator too, but red line reacts to mood better.
If it goes erratic all sessions I would guess you just play too many tables.
One zoom table is supposed to be 4 regular tables, meaning you should handle 16 regular tables.