I think it's related to dopamine, it's what makes you interested in things. I remember I walked into Dominos with a friend to get a pizza once, casually asked about a job advert on the front window, had a 5 minute interview and got the job. I was so happy, my brain must have been flooded with dopamine, I literally ran back home and messaged my friends to make plans to go out.
I've also experienced that from amphetamine, your mood rises, I message friends on Facebook to chat even though I literally never feel like it. Like I literally never just make conversation on Facebook. I need to feel like this more often, I know I should accept that I'm quite introverted, but I'm just way too introverted, I'm a cold, distant zombie, even to my own family sometimes.
Can drugs help? Like antidepressnt SSRIs or NDRIs? I need a solution to my life, I want a social life, I want to be happier at work...