I think every one covered a lot on the different options you can do Eox.
I myself have some sort of anxiety disorder. This is self diagnosed of course.
From what I have learned about anxiety though, it appears to me that a lot of anxiety comes from the inability to meet an idea of perfection.
Every one has ideal images of things but those with anxiety take things to a whole new level. They practically demand themselves to meet unrealistic conditions or an image of perfection
It is their fear of failing to be perfect that drives anxiety. It is their failure to meet their perfect expectations that eventually leads to depression which in turn generates more perfect ideas and the cycle continues.
So I would recommend working with your pickiness on how things are supposed to work… but don’t think about it too much… 
Thinking too much on things is one of the main downfalls of people with anxiety. You think… and think… and think… thinking more and more about perfection realizing you can never meet it.
So the best thing to do to help rebalance yourself I think is to embrace your chaos. Many people have already given suggestions on how to do so.
Just go in and act stupid. People can talk trash all they like but only you really know how skillful you really are. Only your opinion of yourself really should mean something to you. Ignore the rest of us if we are not helpful.
Skill is not just about doing everything right from the beginning. Skill is also about knowing what to do when things fall apart and chaos rules. And the only way to know that some times is to spread a little chaos yourself. But have fun with it.
And make no mistake no matter how stupid an action might seem you can always learn something from it, and with infinite lives you can learn a lot from dumb actions.
Go and play how you want to because you want to not because invisible faces on the internet are idiots.
Hope that all helped some how.
Axiety before playing.
I hope those little tips will help me to feel better while playing. Thanks to everyone who posted here for your support. It really matters to me.
I think people covered pretty much everything, however, so much kindness with 0 idiots smart assing around restores my faith in humanity a little bit. Good job guys.
Eox, since you’re French as well, feel free to add me on steam, we can join a vocal, dedramatize the situation and have some fun pubbing!
I get this with games i play on a daily basis, maybe switch things up a bit play something out of your usual deck of goto games, with no intent on doing well have some fun then return refreshed.
You can warm up the test range (no clue why I’m forgetting it’s name), but I wish it was more difficult tracking wise 
Making another account for practise isn’t actually a bad idea. (I know this is frowned upon) However, it allows you to practise without actually caring about anything since technically you are not on your main account. You might be worrying about ruining your stats and using a practise account could be beneficial if this is the case.
If I may join in, I experience the same feelings as the op, mostly in mobas and ranked modes. But in my case I’ve noticed That The shaking usually happens after The game is over and I get light headed like that match took all my soul to perform.
Though for a long time i have been stuck with the worst Internet um the universe, so that is one reason I get anxios before playing a match. I know i will have min 120 Max 180 ping which Always puts me in a disadvatage compared to most other players.
@Eox I had something similiar when playing CS:GO. I enjoyed it at the end, but before or when playing first few minutes, it was just pain.
I think the overall community there was the reason, so I stopped playing CS:GO completely (I only play arms race sometimes :D)
hmmmm… as a side note. I find it amusing to think of anxiety as like playing a game of tetris…