I'm no expert, however from personal experience I've found that planning little things ahead does a great deal to me as well as keeping a steady pattern of sleep. Whenever I do things I make sure not to rush and if for any reason I drop something or something suddenly happens I don't rush to fix it. In case of stress there isn't much you can mentally do for yourself, but if you fall in a situation where you're feeling very stressed and overprotective or yourself, you could try doing what I do.
Just keep on taking a deep breath even after your lungs have filled up, then keep it in and tense all your muscles all at once and stay like that for 10 seconds without breathing out or relaxing. Once the 10 seconds have passed very slowly relax your muscles and slowly release your breath. This is a way or chemically releasing stress in your body which is caused when you're feeling threatened by things such as deadlines or medical problems.
Interesting idea, very similar to some of my colleagues and I really like it. During my research however I found out that people aged 50 and over are paranoid about connecting their savings or other apps with their bank accounts. I think this will work for people 50 and over who are familiar with phones, but the older generation might do with a physical version, one that doesn't directly connect to their bank :)