It wasn't a last straw for me, it was something that made me feel that losing weight might be a possibility at last. I've been severely disabled for years, I rarely make it out of the house and have to spend a lot of time in bed. My medical condition is made worse by all exertion (ME/CFIDS), it's difficult to stick to a set routine when my energy fluctuates so much, and I was starving hungry all the time.
Then my doctors put me on low-dose amitriptyline for pain. It hasn't done anything for pain yet, but it immediately reduced my appetite considerably. It also caused stomach cramps, but they put me on Buscopan for that - and I've learned to be careful to take it with meals, because if I take it before and then get side-tracked for half an hour before I actually eat, it causes nausea. Anyway, the meds are more or less under control. After a week or so of not being particularly hungry, I decided to take the opportunity to try to lose some weight. Being less hungry made it fairly easy at that point, so I got myself all organised, started thinking about how I should be improving things (snacking after naps was a daft one - the hunger I get when I wake up passes fairly soon), joined FitDay after a week and discovered that calorie counting is actually fun rather than miserable, bought scales after a month once I could see the difference and feel my clothes getting a bit looser. I'm glad I waited for that, though. I've had them for three days, and my weight stayed the same for two and then went up an entirely insignificant 0.2lb. Thankfully I feel secure enough in what I'm doing not to be bothered by that; a month ago it would have stressed me out.
I don't know if the lowered appetite will last (been rather hungrier the last couple of days), but I feel so much more in control now that even if it doesn't, I think I've got myself organised and into much better habits and am determined to see this through. I feel much happier doing this than I'd expected. For starters, indigestion caused by eating too late, eating too much and/or eating in bed (which I need to do through illness sometimes, and then it somehow turned into a habit) is gone! And weirdly, I have a bit more energy!