I get those worries in the middle of the night! What I do to help myself is immediately get specific and see if I can think of actions that might help. For example, I'll be anxious about living alone in my house, being elderly and not able to care for myself and having "stuff" just accumulate around me and being old, sick, dirty, etc. I mean, look at all the dust on the top of the door lintel!
I find what I'm thinking about, what examples I'm giving myself to make my worries make sense (dust on the door lintel) and will decide to do something about them tomorrow, right away, so they can't bother me anymore. I use to worry excessively about my finances and understanding them but started working (a couple years ago!) with my husband and getting more familiar with them specifically and now I'm only half as scared. I recently had a breakthrough where I realized that nothing "sudden" would/could happen with the finances, even if my husband were to suddenly have something happen to him! There would be time to work with and understand what I have and what I need and how it all works.
I think often we have this all-or-nothing idea that suddenly we'll be in the depths of depression and helpless or something but it doesn't really happen like that but more gradually. And I have learned to trust myself to work hard to help myself if I have a problem! If you see you're slipping in mood, there are things you can do at that time; if one is not taking care of one's self and see it, one can work to improve that!