Is it chemical---is it thinking patterns---does one cause the other---these are difficult questions to answer, and I'm pretty sure the balance varies from person to person----
I have found that my thinking often brings on unnecessary emotions. Now, what I'm about to say does NOT mean that medication is not needed in many cases, but as a supplement to treatment. Everyone is responsible for their own decisions.
I don't think it is wrong to point to thinking patterns when dealing with depression. But telling a person to think positively is just silly. They aren't thinking in a balanced manner and they may not even be sure where the break-down is. Like telling a person to exercise and eat better---it's not helpful unless there are some specifics. What kind of exercises, for how long? What kinds of food?
Same with the thinking thing. It's important that a person learn how to isolate exactly where the thinking is going off track. And also to empower them with the knowledge that emotion follows thinking, not the other way around. At least I found this to be incredibly effective.
I used to catastrophize everything. It got pretty ridiculous, but I couldn't break the cycle of thoughts, and so my emotions would rev up as they did.
Maybe I was an half-hour late giving my daughter a dose of medicine. Well this was just unforgivable! I must not love her. Now the medication won't work properly! Maybe she'll get sicker. Maybe she'll die. That would make me a murderer of my own child. I'm a horrible person. I'm worthless. So much better if I wasn't born. I'm the worst mother in the world. If I was dead, someone better could take care of her.
That's pretty ridiculous thinking, but just the kind of cycle I would get caught up in. It wasn't until I learned that I was actually doing that to myself that I could get control of it. It helped me to change my POV. I would imagine a good friend coming to me and telling me the same things I was telling myself. I imagined how I would respond. Then I started responding to myself the same way I would respond to that friend. I was harsh with myself. I forced myself to do this and then I forced myself to listen to the alternative message. The message that said I was not the worst mother in the world, it was only 30 minutes late, she is not going to die because of this, I'm the best mother for her, and getting distracted or losing track was not unforgivable but very human. If being late with the dose REALLY would have meant that she would have been thrown into a medical emergency, then I would NOT have been late. Because I'm capable. Because she is important to me. Because I'm a good mother. And the fact that I would get upset with myself for being 30 minutes late just proves that. I care.
Other things that would get me into trouble was black and white thinking, all or nothing thoughts, and fortune telling. I just learned that most of what I worried about, most of what kept me up at nights, most of what made me want to give up just never happened.
I still fall into this sometimes, but now I have the skills to figure it out and do what I can to stop the pattern. Leaving god-belief behind has been very helpful. I no longer feel the need to scrutinize my every action, my every thought, my every emotion and analyze it and look for where it is wanting or weak or bad. We all need to do this to a certain degree, but when I thought there was some entity in my psyche evaluating my every move, I felt great pressure to look at all the horrible things they would see and try to fix, fix, fix them.
Guilt and fear were my biggest triggers. And yet, most of the guilt and fear was not based on the reality at hand. I learned that just because I feel guilty, it does not mean that I am guilty. It could mean I'm guilty, but I had to be realistic. If I felt guilty, I would actually start to search for reasons to feel that way---and trust me---I would find them. Now when I get some weird guilt from nowhere, I quickly look things over and let most of it go. The guilt follows. Sometimes the reasons are valid, but then I realize I'm blowing it to unreasonable proportions. Only a tiny bit of guilty is necessary, to learn a bit of a lesson, so I can move on better. I don't need to batter myself for days on end for some tiny infraction.