Hi spikes. Whenever I attempted to return to my old job I did so on a part-time basis to slowly work back up to full-time. It sounds like they are really interested in having you back. If you think you could handle part-time better, initially, that could be a bargaining point.

I don't think you necessarily need to explain anything from your past, in terms of health issues. And if you do like the "initial part-time" idea, an explanation need not go beyond "An issue in my life only allows part-time work for a short while, at this time, etc." It would be none of their business what the details are. Just a thought.