I'm a former extrovert turned introvert.
I used to have tons of friends and was really outgoing. Most people have a close personal group of 4 or 5. My close personal group had 23 of us with more around as acquaintances.
For reasons I would rather not go into, I ended up moving away to a city where I knew no one for 3 years. I lived on my own and worked a night shift on my own. I spent my days online. In other words, I spent 23 hours a day by myself.
When I moved back, I found I was no longer outgoing and certainly not social. My conversation skills are non existent and find I would much rather sit in silence with my own thoughts than actually talk to someone.
My close group now consists of 2 people. My wife and my best friend. These are the only two people I can sit and have a perfectly normal conversation with.
Sad isn't it?