Wesley's Psychology

In these journal entries I was struck by how Wesley seems to be thinking and acting in ways that seem quite out of the ordinary (from my perspective). His thought patterns when he wrote of constantly seeking assurance of salvation, and worrying over and over about his lack of joy bring to mind several psychiatric conditions that I am vaguely familiar with. He seems to obsess continually whether his salvation is legitimate, and Outler describes him as suffering from a "spiritual depression" in the months after Aldersgate.  I wonder if there has ever been a study done of Wesley's psychology/psyche and how this impacted his theology and various motivations. Another question is in regards to how similar Wesley's language and thought process is to other Christians at the time. Is there evidence that this way of thinking about salvation was common in Wesley's context? I imagine that a deeper historical knowledge of the religious norms in Wesley's time would help in understanding how and why he acted in the ways that he did.