What causes introverts to lose "energy" in social settings and require recovery afterwards? Over the years I've seen numerous articles about introverts that mention that they dislike large social interactions (meetings, parties, etc) because they drain their energy. These articles mention that it can take days or weeks to recharge this energy. 

This is anecdotal evidence, but I've personally felt it twice in the last week, which peaked my interest. A good way to describe this phenomena is - after a couple hours of large corporate meeting, the energy is gone, and I feel demotivated and just want to go home. "Feeling drained" is another good way to put it. 

Are there scientific theories about what is causing introverts to lose energy in social settings? Is it related to mirror neurons? Is it related to a particular neurotransmitter system in the brain? Maybe it is related to a specific neurotransmitter receptor mutations?

Edit: 

I found this relevant question that asks for the name of the "introverts losing energy" phenomenon. It mentions the following terms:


Social overload
Social exhaustion
Decision fatigue
Over stimulated
My sister and I are both introverts, and have been talking about this before.
We have agreed about the following:


When being social, we feel like we are obliged\expected to do\say certain things and avoid doing\saying others. We are supposed to ...

go where the others go.
be nice and agree rather than say what we think
do the same activity as everyone else
do it at the same time as everyone else
listen to the same music
eat the same or at the same place
etc etc etc...

Our will to do\say what we like\want is challenged whenever we are social. We feel restrained, and We feel that we are unable to relax because we are restrained from doing what we feel like doing. Sometimes being social feels like being at work with colleagues all day - it feels like it's more obligations than our will.
We happen to love some activities that happens to not be a good party activity. Like reading, programming, painting, etc. We need to choose either these activities or being social, and we prefer to have some of both, but we are forced to choose.
When I was a kid I had this dilemma that I wanted to play computer games, but my friends didn't want to. So at my computer I missed my friends, and with my friends I missed my computer. See the problem?
Introverts are just not that interested in talking just for the sake of talking. In my case, I go into different modes: In social mode I will chitchat and spend all my attention to people. In private mode(most of the time) I really don't care to talk unless there's something specific I need to talk about, and then I just space out of every discussion around me. I've never used to be interested in talk that has no clear purpose. It's like why talk if you don't have a point?
When we don't feel like being social this is often partly because our thoughts are focused on completely different things - not on the people around us. My experience (from me, my sister and friends) is that introverts are more interested in inanimate stuff and topics than extroverts are. This might be false, and it might not.
While being social I am mostly unable to really think through anything. When I don't filter out what people are saying, all my thoughts are interrupted and I have a hard time thinking anything logic. I'm not comfortable with this, it makes me feel unsure of my decisions, and I hardly trust my own decisions in this situation.
When I later get back to my private sphere I will spend time thinking through everything again. Make up my mind again for anything I've been talking about, figure out my decisions again for anything I had to decide, and so on.