^ I'd say it's a really good sign that you're feeling oddly mellow
The thing to remember is that what goes up must come down, what begins must end, what expands must contract. There is a cycle to life that is pretty much what it is. You really can minimize the bumps in the road, but change is inevitable. And it is not always welcome.
What you
can always control (given a certain amount of skill, from practice) is your reaction to what's happening. And more often than not, that is the difference between a good day and a bad day.
Btw, stress (and it's an issue for me too) is the result of not being fully present, of pushing to get somewhere you're not. The solution is to relax and align yourself with the flow that will take you to where you want to go. It's kind of like a martial artist who can just tap, and down the opponent goes. Because of a lack of skill we typically expend way more effort than necessary, and in the process we literally wear ourselves out (stress is superhard on the body).