When I experience this I call it my "mental plateau". I get content with the goals I have achieved and so I start thinking that I can forgo reaching the "big goal". The problem is that the weight begins to creep back on as you become more content and you start returning to new habits.
Perhaps you should just go into the maintenance portion of the SP program and if you have discontinued working out then get back into that. Start back on small goals that you may have tossed aside like drinking water, eating more fruits/veggies. It won't do any good to try and get back on a full blown weight loss eating plan if you aren't motivated. Just do what you can to maintain the progress you have made and I would bet that within a month or 2, you will break through this mental plateau.
If you don't love your body now, you won't love it after you reach your goal!!!