Yes, it is a habitual tendency, a karmic propensity. Over the
past few days I felt a little depressed too because of workload and
lacked sleep, all these are karmic propensities and habitual
tendencies surfacing due to the conditions.. But they didn't last
long because if you know the right way to practise, you will not
keep being pulled into the subconscious momentum. Mindfulness can
'pull' you back.
Whether it is from past life or this life doesn't matter, but in
Buddhism, we must be aware of this habitual tendency and karmic
propensity and not give continuity to it. Sometimes chanting,
listening to music, relaxing can help. Chanting is also a good
practise to deal with these propensities... so is sitting
meditation. When you feel depressed, sometimes it's good that you
just pause for a while, maybe for 5 or 10 minutes, just pause,
relax, and do some chanting or awareness of breathing meditation.
It helps a lot.
When your mind has clarity, the dark and depressed feeling will
dissipate, and your mind will feel bright, alive and joyful. Same
as what I said in the other thread, you have to practise and see
the results for yourself. If you never practise it is difficult to
comprehend the dharma and how it can help you. If your mind has
'brightness' you will not feel the same.