Concerning the time question, Conviction of sin is usually during a short time such as a sermon and/or a short time thereafter (within a few weeks). Is depression usually much longer? Or put another way, is long time bad feelings about yourself and your situation usually depression rather than conviction of sin by the Holy Spirit?
A sermon might make me think: I should search the scriptures and see if the preacher is applying correctly what he read onto facebook. I call that conviction. In essence, conviction is something that makes me look at my life in the light of scripture, whether it be the Sunday sermon, or the still, small voice of the Holy Spirit.
Depression on the other hand, doens't invoke scripture, doesn't make me think in terms of scripture and most times what I feel guilty about isn't something warned about in scripture or contradictorily is something one sees as sin in someone else's life, but refuses to recognize in one's own life.
One thing that I "normally" feel guilty about while depressed that I am matter of fact about any other time is clothing. We have certain $$ set aside for buying clothes. I am an excellent seamstress and can make, remake, repair or redecorate anything made from fabric. It's a God given talent. My children aren't dressed in "designer' clothes, but neither are they shabby. But let me get depressed and OH MY, nothing is good enough. And I feel guilty because I can't spend hundreds buying them brand new wardrobes, that I WOULDN'T buy if I weren't depressed. See, depression is often illogical.
I have another "normal" thing and it has to do with food. One of my first signs that I am dipping has to do with how I feel when I go grocery shopping. Not depressed: I make a menu, make a grocery list and we cooked for a month on what I buy. Its economical. Depressed: I havne't the energy to make a list much less cook (which isn't my fav thing to do anyhow) and then we end up with not much real food and we spend more $$ on eating out or convenience food. What's contradictory about that? I will believe that my children are being deprived by not eating out. It's not the truth, my kids will only eat out so many time before they start complaining that they want "real" food. But what my mind believes is different.
Now, my mother's first sign that she is dipping is when she starts talking drug use in the neighborhood. Notice, she is addicted to drugs herself, but she condemns their use by the neighbors! The difference according to her is that she has a perscription and they don't. ooooooKay.(btw, the neighbors aren't really dealing/using drugs, this is something she imagines when she becomes depressed) Now I should warn you that my mother's official diagnosis is: depression with paranoid schizophrenic tendencies. So she is dealing with more than just the depression, but the schizophrenia didn't manifest in her until she'd spent years selfmedicating the depression and wasn't a continuous thing until her 60's. (by continuous I mean she used to have episodes of paranoid off the wall behavior, that once treated disappeared for months or years without medication, until she spiraled again. However, since her early 60's she's had to take antiphsycotics continuously along with the treatment for the depression)
The difference between my mother and my depression is this: I have episodic depression. After my last two babies I had to be treated for a couple of years (each time) before the depression subsided. Since then (my youngest is 12), I've had a couple of other episodes that needed medication and both of those times I was able to wean off the meds after about 18 months or so. Right now, its been about 6 years since I've had an episode, though right at this time it is on my schedule to talk to my doc about starting the meds again because I am not handling my arthritis pain as well as usual and my family tells me I am in a 'bad mood' all the time, even when *I* don't think I am in one (I get angry a lot when I'm depressed). My husband and children know my history and are often better at seeing problems early than I am, so I take them seriously.
My mother's depression, on the other hand, never goes aways. I can't remember a time from when I was VERY young, that she wasn't depressed. It was better when we lived "up north", because she had a support system up there of friends and family that understood her and we socialized with quite often. But when we moved to Alabama, even though she had family here, they were the family she'd gone up north to get away from! It was here that she got hooked on perscription meds.
Support systems are another subject that is very important. Depressed people often isolate themselves because they think that "no one will understand" or "if I tell X what is going on they'll laugh at me, or tell me I'm crazy or condemn me or......" People who are prone to depression NEED family and friends that they can trust to listen while they cry, to not condemn but expect that the depressed person will seek treatment and to hold them accountable once treatment has been prescribed in actually following the doctor's instructions. Not only will my husband and kids ask me if I've had my meds (when I'm on them), but I have good friends who'll do the same thing! (of course the depressed person has to accept the support or all for naught)
HTH