How to not play tilted in OTB? Advice needed

Today in an OTB tournament I lost a game where I lost a superior position because of a blunder, and that loss carried over to my next game in which I played with little effort and less motivation as I was still mad from earlier. I ended up losing that round too, as I was just blitzing out moves not caring about the game, still mad about the previous game. Any tips on how to fix this negative attitude and how to remain positive and concentrated in an OTB tournament even after a horrible loss? On online I don't care early as much if I lose OTB, I hate losing over the board and I feel like there is much more at stake. I just want to have fun and enjoy chess without pressure, but I can't be able to do so after I lose. So I guess my question is to those who have OTB experience... how do you maintain your composure after a horrible loss in a game you should have won? It's really tough for me.

Guess you need to learn to let go of the past and to not let it define your future

I too experience this. Recently playing in a OTB rated USCF tournament, I was winning my rd 1 game. I was up material and had superior postilion. My opponent knew he had lost but prolong the match by just sitting there for over 30 minutes. the time control was game 90 with 30 sec increment. I became annoyed and got up to stretch my legs. Shame on me but I lost focus. Ended up losing my advantage and even an opportunity to force a draw. Needless to say I lost the game. I was so piss with myself that it carried over in to my rd 2 game in which i played horrible. I resigned. Having a short memory in chess tournaments is hard.

Sometimes it is best to withdraw in such situations. If you cant do that physical exercise might help.

Why did you blunder in the 1st game? Did you have enough time left? Did your thoughts wander off? Think about your move, decide about it, then check it is no blunder, then make the move.
Why did you blitz in the 2nd game? That is a sure way to lose.
You should turn the pain of the loss into a positive desire to win even more in the next game: think longer and play more accurately without any blunders.
Never drop out of a tournament, play on despite losses. It should motivate you to get better.

I have a DWZ index of 225 so this means 225 evaluated tournaments. A whole league season or an "IM tournament" in Budapest with 11 rounds counts as 1...

So in other words: age, experience and practicing will do the job. Just plan your next otb encounters! :)

Personal note: I find it personally worse if this a happens in a lone game, say a final, last round, isolated game and I cannot play soon after that. Playing the next round is a blessing, then you have the chance to make it better and forget about the previous games.

I agree with @Sarg0n here.
I too have played quite a lot of tournaments and for me every round feels like a new chance to play a good game.