Whether you had a "good" or "bad" breakup, bumping into your ex can be an emotional experience. Don't be surprised, it's totally normal to feel a whole range of emotions when you see someone you were once close with... and now they're just somebody that "you used to know." (You didn't have to cuuuuut me oooooff)
When we bump into someone we used to love, our brain starts to send signals to the rest of our body and make us feel certain things. Let's start from the beginning and analyze this phenomenon in a scientific way.
When you first end a relationship, your hormones push you to make terrible decisions whether it's getting unreasonably drunk or completely changing your hairstyle. These same hormones are responsible for making you feel wonderful when you fall in love.
When you stop a relationship with someone you truly care about, stress hormones (cortisone and adrenaline) get released in your brain and that, in turn, triggers physical reactions such as nausea and respiratory problems. You know that feeling when you just want to stay in your bed, ache in pain, quit your job and be miserable because "nothing matters anymore." That's your hormones being shitty.
A research from Rutgers University showed that a post-breakup brain activity can be compared to an addict going through cocaine withdrawals. Wow, intense. In other words, when we fall in love, we become "addicted" to the other person just like an addict gets addicted to drugs. Yikes!
Now, depending on how soon you bump into your ex after the breakup, your brain will have different reactions. Criminologist Brian Boutwell from Saint Louis University says that people eventually recover from heartbreak, "The pain will go away with time. There will be a light at the end of the tunnel." Meaning if you bump into your ex years after your breakup, chances are you won't feel a thing. Nothing.
If, however, your heartache is still fresh, your brain might react in VERY passionate ways. Whether you like it or not, memories of past experiences get triggered. Normally, when you see someone you love, the release of neurotransmitters makes you feel really good. After a breakup, however, you can't get a physical reinforcement needed to "feel good." For example, you can't go hug your ex once neurotransmitters are released. As a result, you end up repressing your brain's signals, which confuses your body and creates powerful physical aches.
Emotional love torments are known to activate the same brain regions as when you physically get punched. That's why you end up feeling stressed, nauseous, dizzy and overall unwell when you bump into your ex.
Specialists say that paracetamol seems to help ease the physical pain, while talking about emotional troubles helps with the other side of the problem.
Bottom line - try and avoid seeing your ex after a breakup. Give your heart some time to heal.