I feel like your title, text and spoiler are talking about three different things. There are many types of anxiety that can be tackled differently.

You already got good tips for most, so I’m going to concentrate on your spoiler text: When you are too high, I recommend chewing coffee beans. They act calming on those cases.

As for your existential anxiety: You might want to continue that train of thought to it’s conclusion: Eventually everything ceases to exist. Nothing is permanent. Everything is in flow. All that is, all that matters, is now. This moment. And all you need to do is live it.