One thing I've learned, in the course of the nearly twenty years since I first became acquainted with Buddhist thought and practice: the act of clinging to a thought, a feeling, a physical sensation, serves only to increase the suffering it brings. Let's say...
... you think: my boss is impossible to work with;
... you feel, emotionally: nothing but anger and frustration;
... and you feel, physically: I'm totally exhausted...
Experience tells you that if you cling to that thought and those feelings, you succeed only in giving them greater power. The boss becomes more impossible, the anger and frustration build, the exhaustion gets to be unbearable.
BUT... if you fight against them, your obsession with them increases and, again, they become still more powerful.
AND... if you try to deny them, they pop up, annoyingly, some other form: a belly ache, sudden bursts of inexplicable anger, "accidents."
So the thing to do is NOT to fight against them or deny them, but rather acknowledge them and let them go.
Acknowledging them is the easier part. Yes, I have this thought: my boss is impossible to work with (or whatever other thought you are obsessing over.) Yes, I am angry and frustrated. Yes, I do feel exhausted.
That part is easy.
The hard part is the letting go. Here's where practice comes in. It's possible, with practice, simply to close your eyes and bring the attention to the breath, and use the natural breath energy to release the stress from first the body, then the brain. It's possible to create a kind of space and stillness in the mind in which you can actually look at the thought, the feeling, the physical sensation... and let it go.
Think for a moment: what happens naturally, as a matter of course, to a thought or feeling, when it arises? Unless you pick it up and meddle with it, it fades away and makes space for the next one. The same with feelings and physical sensations. Their natural condition is ephemeral. They come and go. All that's needed (simple, as I often say, but hard!) is to let them be their natural selves, and disappear.
There's another thing that you can learn with practice: how, once you've acknowledged them, you can back away from thoughts and feelings. It's an almost physical sensation in itself, the backing away. It's as though you put yourself in the balcony of the movie theater of your mind, and watch what's happening on the screen without thinking: that's me, that's mine, that's who I am. You get to be the neutral observer of your movie, not the hero--or the villain!
(By the way, that's a great mantra, if you find the mind wandering and need something to anchor it: this is not me, this is not mine, this is not who I am. If you keep repeating it, it will give the mind some occupation other than wandering off and doing its own thing. You could try it in the car, on the way to work. Much better than fussing over the anxieties!)
None of which is easy. I still don't find it easy after twenty years. But the alternative is, what...? More suffering.