At the advice of my doctor I took a medical leave a little over a month ago to see if some of my physical symptoms of illness were caused by stress at work (other lifestyle changes were helping but not completely). During the time I've been away it has become apparent that my work environment was indeed making my physical symptoms not heal and I will not be returning. I am one of many (call center type customer service) and the advice on the "how to resign" podcasts would be considered taken care of as I left for leave as if I was leaving completely (desk clean, all outstanding items taken care of) as part of the exercise of de-stressing.

Knowing I did not want to return I tested the market for other positions and have been given an offer. My question is how do I resign gracefully? I won't be returning to work because this wouldn't be healthy. Should I go to the office and hand in a letter? What other suggestions would anyone have?