I don't have any advice, but wanted to say that I have had a similar issue with my 6 year old daughter. She has always been sensitive, but it seems like her ability to control her negative emotions has suddenly eroded, and then she feels rotten about herself because she doesn't like her crying, falling-apart self either. ("Why did I do that? WAAAAH! I hate myself!")
I talked to her about it and asked her for ideas about how she might control herself in the moment, and she suggested that every time she could potentially cry about something and doesn't, perhaps I should give her some candy, and then she would put it in a bowl, and at the end of the week, she could choose any piece she wants.
Ha. No. I pointed out that if she can stop herself for candy, it is within her control to stop herself, period. But she did have a point, which is that for her, rewards work very well, even if the only reward is my noticing every time she doesn't dissolve into tears, and giving her a high five. For some, it might be coddling, but when I stepped up the punishments for awhile it seemed to make things worse.