On top of the depression I have PTSD, anxiety (panic attacks, albeit rare) and social anxiety.

It was my counsellor that informed me of the PTSD from a childhood event. I wonder whether the social anxiety and depression are linked. On the rare occasion when I'm not depressed, I feel I could tackle anything and conquer the world, yet when I'm depressed, the concept of socialising or having to make small talk with people terrifies me.