This post is very helpful, as sometimes, I may dwell on things that haven't happened, or most likely will never happen. Mainly with work. I don't know why, really. Perhaps, it's just become a habit. I know that I shouldn't be dwelling, but I do. As if worrying in and of itself will magically make everything turn out well.
I like what you're suggesting here - that happiness isn't meant to be a continuous state. Yea. That could be the problem, with our culture in general - believing that happiness must be a constant, or something is gravely wrong with our lives.
I need to dig deeper, but what does stoicism say about mourning/grieving? In my opinion, there are major life events whereby we must experience things on a purely emotional level.
I don't know what Stocism says but it doesn't matter.

"We" don't need to follow rules in that sense. You can be "stoic" where it's a good response and mourn where that's a good response. That's what most people do.
You aren't likely to go to a funeral, find your friend there who would like to cry but can't because he is a "follower" of Stoicism.

He may not be able to cry at the same point that you would cry but that's just a difference in individuals, culture, customers, preference, etc.
I have a friend that I climb with (female). She took some course (I don't know what it was called). She had to pay quite a bit, she always tries to get others to sign up for it (pyramid thing it sounds like to me) but she says it has helped her a lot.
From watching her, being around her and talking to her, it has mainly made her more responsible to herself and act in a more positive way. She has even become a "coach" for whatever this program is in addition to be a school teacher.
In the past, when we were climbing, when I'd suggest a harder route, she would frequently say "I don't think I can do it, I don't want to try, etc". Now that she is involved with this coarse, when she gives that kind of a response I say "That's not very coach like or positive is it?". She'll laugh, think about it for a second, agree, and then try that route. When she tries a route, she generally completes it as well.
I have noticed her becoming more confident and positive. I asked her if the class was mainly females as that would be my guess. She said "Well, there are a lot of female Real Estate agents in there".
It's like self-help books. Call me sexist (I'm sure you will)

but most of them are purchased by females. Courses like this are mainly taken by females. It's probably just a cultural thing but females in our society seem to have more self-doubt than the average guy.
I'm not implying that they have more to improve upon, it's probably the opposite, but they are more sensitive to it. Most/many guys are confident (whether they should be or not is another subject) and just don't need help in that particular area.
I think that's all that is going on with you. It's partly a cultural thing and partly an individual thing of course but it sounds like you have every reason to be confident and sometimes you aren't. When things go well for you, you start to realize that you have no reason to not be confident.
Guys just seem to come upon that realization more easily. I do know guys who aren't very confident of course but compared to females, their numbers seem to be much smaller.
The tables turn however if the subject is can you express or discuss your feelings.

Most women win hands down here just as they are in the minority where "confidence" is concerned IMO.