Hi lackoffocus,
In my opinion it doesn’t sound like you have depression per se. I have been in similar situations myself. The fact that at times your able to be driven and then other times lack focus is relatively normal. The stumbling bock seems to be the putting it together - the accomplishing and succeeding part.
There could well be a unconscious’s reason for this. I myself feel when I use to miss deadlines for silly reason is because I had no self believe and didn’t believe I deserved to be successful.
Maybe your not happy with your life at the moment and this is unconsciously causing you to ‘###$ things up’. If this is a common occurrence for you maybe you have a touch of Self-Defeating Personality Disorder. Don't beat your self up over it, the unconscious is a cruel mistress. I would suggest seeing a therapist, after all ‘there no such thing as laziness’.