How do I keep myself from overreacting?

Take a few seconds/few minutes time out to just breathe. Sometimes taking a little step back can put things into perspective. However it can also be hard to teach yourself to do this. It might be good to try practising taking some time out in your day to day life - such as 5 minutes to sit and just breathe so you have had practise before a sitatuion arises where you may need to use this skill. :)

Try to identify your thoughts and validate them.. Analyse them and put yourself into the situation as a listener/ observer..

It depends. I saw some people overreacting, because they don't trust themselfs enough, therefore expects others to also see them badly. Any coment, any move is percieved as an insult, because person is so scared and harsh on themself, that can not believe others have positive or neutral feelings about them and don't intend any harm. I would suggest to start learning to love yourself and trust others, that they love you too.

A lot of times, you have to practice listening to yoiuyr thoughts. That is where you can unconsciouslybegin making a mountain out of a molehill. Try to rationalize with yourself, and ask if it really will affect you that much. Or think of what you would think if the event happened to anothwer person.

Whenever a situation occurs where you feel overwhelmed or confused, try to see yourself as an outsider and perceive your own views upon yourself. Based on those views try to act appropriately.

Think how much you care about yourself and others and the stress you put yourself trough. Visualize your self calm and smile.

I usually try and put myself into the mindset that 20 years from now whatever feels like the end of the world right now might not seem so bad.

When you feel you are , pause , breathe , wonder if it's worth all the stress. Otherwise yoga , meditation and a balanced healthy meal can bring down your stress.

By trying not to act on your first emotion, take a few breaths and think of how it really makes me feel and impacts me, usually things aren't as bad as they first seem :)

Just Calm down. Don't think like you have a undefeated problems. Everything is gonna be fine. Just calm.