I have only felt emptyness when my PMDD symptoms are flaring up, not during depressive episodes so perhaps it is different. Its not pleasant but since it is not a constant thing for me I just wait for it to pass. I do try to get on the bike so I can feel my heart beating and know its not really empty in there. Is there a trigger for this mood shift? Is the stress in your life getting too much? Can you ask your support network for some help? The more you do now the less severe the episode is likely to be.