I'm much more socially confident online. Online there's no pressure of speech. I can take my time to stop and think and work out what I'm going to say. In real life, in real time, I'm more likely to say something stupid and embarrass myself, or not be able to think up anything to say at all.
I find it very difficult to become comfortable with people, and I have to get to know people quite well before I'm able to hold a normal conversation with them without becoming flustered and nervous.
It takes experience to become fully aware of the true double nature of the word 'petrified', it can refer to wood that has turned to stone, or to fear. I've found that when I'm thrust into social situations with strangers, I tend to shut down, sitting quietly, not speaking, not making eye contact. As though I've turned to stone.
So there's social anxiety, which lends into depression when I begin hating myself for not being able to be interact 'normally', and there's also general self-loathing, when I over-worry about how people perceive me, and find it impossible to forgive myself for the smallest mistakes. I sometimes find myself inwardly scolding myself and hating myself for tiny embarrassments which happened years prior and that surely no one else remembers. The hard part is in learning how to let that stuff go.