The 'Primordial dot'
Trungpa wrote an interesting article in whic this is mentioned called "Working with Early Morning Depression."
http://www.shambhala.org/teachers/vctr/ges.html
The best way to work with this form of depression is to uncover our 'spark of basic goodness.' Instead we think up all sorts of escapist remedies. One that seems particularly prevalent nowadays is what Trungpa calls 'the setting sun.'