Romantic rejection can be one of the more painful experiences, and that's because "our brains love to be in love," Elisa Robyn, PhD, a consultant who focuses on heartbreak, tells Bustle. "When we are in love our body releases phenethylamine, dopamine, cortisol, and oxytocin." And it's these chemicals that make us happy, and keep us focused on the person we love. "Food tastes better, the day looks brighter, and we feel stronger," Robyn says.

A breakup means these love hormones are no longer the primary chemicals in your brain — and that can be very uncomfortable physically and emotionally. "Now rather than being bathed in loving feel-good hormones, our brain is soaking up cortisol and epinephrine," Robyn says, which are the heart-pounding "fight-or-flight" chemicals caused by stress. And that can be a tough transition to go through.

Cortisol, along with adrenaline, are also released into the body after rejection. And, as Robyn says, "too much cortisol will swell our muscles, which are preparing for 'battle.'" Again, this is due to fight-or-flight response, which means your body is reacting to a stressful change and trying to figure out what to do.

Muscle swelling is what can cause physical pain after a breakup — like aches and soreness — and it's why Robyn says running, walking, or working out can help you feel better.

"While blood is going to our muscles to prepare for 'battle,' blood is not going to our digestive system," Robyn says. "This can result in the classic nausea and inability to eat symptoms," both of which can occur after a major rejection — like a breakup.

Exercising and moving can help with digestive troubles, Robyn says. So even if you don't feel like going out for a walk, or popping into the gym on your way home from work, it really can help you feel better.

Again, that "heartache" feeling is a very real side effect of rejection. "Rejection can feel physically painful because it follows the similar neural pathways in the brain as when we are physically injured and in pain," Zhang says.

Heartache can obviously occur at the end of a romantic relationship, but also if you're rejected by friends or family. "In terms of social rejection," Zhang says, "the difference may be that these painful memories are more easily held in our amygdala and hippocampus, which are our memory [centers] in the brain. So, similar experiences of social rejection will bring up those memories of pain and amplify the pain response."

The brain may do itself a disservice by ruminating on the emotional pain you're experiencing, in the same way it might fixate on physical pain, like a stubbed toe or broken arm — when those things happen, it can be tough to think about anything else.

"Rejection is hard on both the brain and the body," Jackson says. "As with physical pain, the brain prioritizes the pain of rejection which is why your mind ruminates on it. And the same brain regions that are activated when you are rejected are activated when the body is in physical pain. So, your brain is literally in pain."

Rejection can be difficult emotionally because it forces you to consider options you may not have wanted or cared about. And many times, that works to increase your negative feelings.

"The ideas and thoughts we form around relationships are quite interesting because in relationships we build mental maps to help us set expectations and plan things out," Zhang says. "What usually ends up happening during rejections and ghosting is that the idea of that person is destroyed and the mental maps we’ve built are shattered. That is challenging for individuals to reconcile reality to their ideals."

It can be made easier, though, by talking to friends or even going to therapy. Through that process, you can focus on creating new plans, while also having an easier time coming to terms with the rejection.

According to Robyn, loving relationships can be addicting in the way they saturate your brain with feel-good hormones and make you feel happy. So it makes sense that, after a rejection, you might go into a form of withdrawal.

"We also lose the physical closeness that we have in relationships, as well as the companionship," she says. "Our brains are confused and lonely. We might be forgetful and unable to focus. This is in part because we are trying to recreate the feelings and generate the hormones we have lost."

This is, again, like an addiction. "In fact, thinking about our ex can give us a small dopamine hit," Robyn says, "which keeps us thinking about our past."

It's not uncommon, after rejection, to go through a period where you just aren't yourself. And that can manifest in the form of brain fog, as well as other symptoms like irritability, headaches, and even phantom pains, Dr. Cali Estes, a mental health expert and life coach, tells Bustle.

It may sound too good to be true when you're in the thick of things, but purposefully going out and having fun can be a big help. "Ways to overcome this are using exercise [...] and getting out in the sun and having a good time," Estes says. "The idea is to keep your mood lifted so that you don’t feel sad or that you are missing out, [which can] lead to anxiety and frustration."

"Rejection results in hurt feelings and sadness and can heighten anxiety and depressive symptoms," Jaclyn Lopez Witmer, a licensed clinical psychologist, tells Bustle. It can also impact self-esteem, and lead you to look for reasons why you were rejected.

"Someone who tends to struggle with self-esteem and self-worth may feel unlovable and generalize to other relationships in their lives," Lopez Witmer says. "This, of course, can be dangerous, and it’s why it is so critical to talk to friends, family, and/or a therapist about what happened to hear alternative perspectives and most importantly, be reminded of how loved and supported [you] are, that this is so hard and it sucks, and that [you] will get through this."

There's no denying that rejection — in any form it takes — can be difficult. Due to the way it changes your body, you might even experience physical and emotional pain. But there are ways to get through it and take good care of yourself, until you adjust.