I can empathise with this completely, I have a similar personality to that you described.
You mention that depression can be easily mis-diagnosed and I have to say my experience is that it definitely can be. I was diagnosed with depression a few years ago, given medication and sent for counselling. I completely believed that I was 'suffering from depression' in the sense that I had an illness, but in hindsight I'm sure I was just 'depressed' in the sense that I was having a bad time of it. I didn't take the medication I was prescribed because I was scared to, and counselling sessions took forever to be organised so I never went. This was because by the time I got the letter confirming them, I felt OK again, and have never since felt like I did then. At the time my mum had a terminal illness, I'd given up University to help look after her and was stuck in a dead end part time job earning a pittance, was living at home again, had split up with a girl and had no time to meet anyone new. It was no wonder I was depressed, but it was circumstantial not an illness. My mum passed away, I grieved and then got on with my life, went back to Uni etc. It scares me how quick the doctor was to tell me I was suffering from an illness and needed pills when the last 9 years tell me that i'm just a slightly introverted character who was having a bad time of it for a few months.
I want to be very clear here that I'm not suggesting depression or anxiety are not real. They most certainly are, and people close to me really suffer from them. That's one of the reasons why i'm so sure I didn't/don't suffer from depression myself, the way I see some people crippled by mental anguish tells me that I don't have anything like the same condition. Personally, I hate the way that internet memes etc have reduced something like anxiety to a case of 'do you hate it when people laugh at you? do you find it really difficult to walk into a room full of strangers and start chatting to them all? do you sometimes doubt you're doing the right thing? you've probably got anxiety' when actually everybody feels like that at times.
Please nobody take me saying I didn't take my prescription and was fine as a suggestion that you should do the same. These conditions are real and I know that medication can help sufferers immeasurably. I'm simply regaling my own experience, not trying to demean or diagnose anybody else.
I totally agree, "circumstances " can combine all at once, to make your life almost impossible for a while, plus we`re ll different and handle things differently.