My wife suffers from this. It's called clinical anxiety and depression, with a heavy dose of ADHD. She needs medication to keep it in check, and some days, even that's not enough. Trying to get her out of the house every few days is like pulling teeth.

On top of that, my wife is an introvert by nature, but you'd never know in a social setting, as she will talk everyone's ear off all night long. I found out that's her nervous tick; when she feels the social anxiety kicking in, she just lets the ADHD take charge and will run her mouth non-stop. When she gets home from any social event, even just a quiet evening hanging out with a close friend, she'll collapse from exhaustion and sleep for half a day afterward.